This spaghetti squash casserole has become my go-to quick, healthy and no-hassle dinner. With tender spaghetti squash, creamy ricotta and mozzarella, and savory mushrooms and spinach, this dish has become a household favorite! It’s so easy to throw together and bakes beautifully, so what’s not to love?
This post contains helpful tips and tricks! If you’re in a rush, please use the “Jump to Recipe” above!
💭 Why you’ll love this recipe
- Healthy and flavorful. I love to sneak wholesome and hearty veggies effortlessly into this cheesy casserole recipe!
- Make ahead-friendly. This creamy dish can easily be made at least three days in advance, perfect for meal prep, parties, and special occasions.
- Perfect for a low-carb and keto diet. This dish is vegetarian and uses low-carb ingredients, making it a delicious and satisfying keto-friendly meal.
📋 Ingredients and notes
To make cheesy spaghetti squash casserole, you’ll need a few simple ingredients. Cooked spaghetti squash, olive oil, a small onion, garlic cloves, white button mushrooms, fresh spinach, ricotta cheese, mozzarella cheese, dried oregano, salt, and pepper. Finish it off by garnishing it with fresh basil leaves!
Variations & Substitutions
- Spaghetti squash. Use a medium-sized spaghetti squash to get the perfect portion needed for this recipe. Properly cut it in half then cook spaghetti squash halves in the microwave before shredding it into strands.
- White button mushrooms. You can use cremini, portobello, or shiitake mushrooms as a substitute.
- Fresh spinach. If you don’t have fresh spinach, you can use other leafy greens like kale, Swiss chard, or collard greens.
- Ricotta cheese. You can substitute ricotta cheese with cottage cheese or cream cheese for a similar creamy texture.
- Mozzarella cheese. You can use shredded fontina, provolone, gruyere, or cheddar cheese as a substitute.
📖 How to make spaghetti squash casserole
Step 1:
Preheat the oven to 375°F (190°C) and grease a casserole dish with olive oil or cooking spray.
While oven is preheating, cut the spaghetti squash lengthwise in half, scoop out the seeds, and lightly season with salt and pepper.
Then, place it cut side down in a microwave-safe dish, and microwave on high for 7-12 minutes (or until fork tender).
Don’t want to microwave? You can also make spaghetti squash in the Instant pot, air fryer or even slow cooker.
Step 2:
In a large skillet, heat olive oil over medium heat. Add the onion and cook until translucent, about 2-3 minutes. Stir in the minced garlic and sliced mushrooms. Cook until the mushrooms are tender and browned, about 5-6 minutes.
Step 3:
Add the chopped spinach to the skillet and cook for an additional 2-3 minutes, or until the spinach wilts. Season with salt, black pepper, and dried oregano. Remove from heat.
Step 4:
In a large mixing bowl, combine well the cooked spaghetti squash strands, ricotta cheese and half of the mozzarella cheese.
Step 5:
Spread half of the spaghetti squash mixture evenly into the greased baking dish. Layer the sautéed mushroom and spinach mixture on top.
Step 6:
Spread the remaining spaghetti squash mixture over the cooked veggies.
Step 7:
Sprinkle the remaining mozzarella cheese over the top of the casserole.
Step 8:
Cover the casserole dish with aluminum foil and place it in the preheated oven. Bake for 20-25 minutes, then remove the foil and bake for an additional 10-15 minutes, or until the top is golden and bubbly.
Step 9:
Allow the casserole to cool slightly before serving. Garnish with fresh basil leaves and serve.
👩🏽🍳 Tips for the best spaghetti squash casserole
Top Tip
Baking covered with foil at the beginning helps cook everything through without drying it out. Removing foil allows the top to get crispy and golden.
- Season the spaghetti squash before cooking. This adds flavor to the squash itself, enhancing the overall taste of the casserole.
- Let the mushrooms sit without stirring for a few minutes at the beginning of sautéing. This helps them brown and develop flavor.
- Allow the casserole to rest for a few minutes after baking. This helps the layers set, making it easier to cut and serve without falling apart.
👩🏽🍳 Troubleshooting FAQs
Make sure to let the cooked spaghetti squash drain and cool, and press out any excess moisture from the spinach before adding it to the dish.
Cottage cheese or a mixture of cream cheese and Greek yogurt can be used as substitutes for ricotta cheese.
You can add bell peppers, zucchini, or kale to the casserole for extra flavor and nutrition. Sauté them with the mushrooms and spinach before layering in the casserole.
🍴 How to serve spaghetti squash casserole
Spaghetti squash casserole can be served in different ways! Serve it as a side dish with your favorite main dishes. It’s also delicious served with garlic bread or crusty bread, roasted vegetables, and a light soup (like this Tuscan bean soup)
🍴Storage and reheating suggestions
Store leftover spaghetti squash casserole in an airtight container in the fridge for up to 3-4 days. Reheat individual servings in the microwave or oven until heated through.
To freeze, allow the casserole to cool completely, then wrap it tightly in plastic wrap or aluminum foil and place it in a freezer-safe container or bag. It can be frozen for up to 2-3 months. To reheat, thaw it overnight in the refrigerator or place it at room temperature for a few hours and then bake it in the oven until heated through.
🍴 More spaghetti squash recipes
If you enjoyed this recipe, check out these other spaghetti squash recipes:
Spaghetti Squash Casserole
Ingredients
- 2 tablespoons olive oil, extra virgin
- 1 onion, small, chopped
- 2 cloves garlic, minced
- 8 oz white button mushrooms, sliced, approximately 2 cups
- 4 cups fresh spinach, roughly chopped
- ½ teaspoon salt, adjust to taste
- ¼ teaspoon black pepper, adjust to taste
- 1 teaspoon dried oregano
- 1 spaghetti squash, medium, cooked and shredded into strands
- 1 cup ricotta cheese
- 1 cup mozzarella cheese, divided
- 1 tablespoon fresh basil, for garnish
Instructions
- Preheat the oven to 375°F (190°C) and grease a casserole dish with olive oil or cooking spray.
- In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add the onion and cook until translucent, about 2-3 minutes. Stir in the minced garlic and sliced mushrooms. Cook until the mushrooms are tender and browned, about 5-6 minutes.
- Add the chopped spinach to the skillet and cook for an additional 2-3 minutes, or until the spinach wilts. Season with salt, black pepper, and dried oregano. Remove from heat.
- In a large mixing bowl, combine well the cooked spaghetti squash flesh, ricotta cheese and half of the mozzarella cheese.
- Spread half of the spaghetti squash mixture evenly into the greased casserole dish. Layer the sautéed mushroom and spinach mixture on top. Finish by spreading the remaining spaghetti squash mixture over the vegetables.
- Sprinkle the remaining mozzarella cheese over the top of the casserole.
- Cover the casserole dish with aluminum foil and place it in the preheated oven. Bake for 20-25 minutes, then remove the foil and bake for an additional 10-15 minutes, or until the top is golden and bubbly.
- Allow the casserole to cool slightly before serving. Garnish with fresh basil leaves and serve.
Notes
- Let the spaghetti squash cool completely before mixing it with the ricotta and mozzarella. This prevents the cheese from melting too soon.
- Sauté the mushrooms in batches to avoid overcrowding the pan, which helps them brown evenly and develop a rich flavor.
- When spreading the spaghetti squash mixture in the casserole dish, press it down lightly to create an even layer for better texture.
- Bake the casserole on the middle rack of the oven to promote even cooking and prevent the bottom from burning.
- Allow the casserole to rest for 10 minutes after baking before cutting into it to help the layers set and hold together better.
Nutrition
Nutrition information is automatically calculated, so should only be used as an approximation.
Yum!