Preheat the oven to 375°F (190°C). Lightly grease a 9x13 casserole dish.
Toss the cubed butternut squash with olive oil, salt, and pepper. Roast on a sheet pan for 25 minutes or until tender.
While the squash roasts, melt butter in a large skillet over medium heat. Sauté onion until soft, about 5 minutes. Add garlic and chopped sage, and cook for 1 minute.
Add chopped kale and cook until wilted, about 2–3 minutes. Stir in nutmeg and cinnamon.
Stir in milk and shredded cheese, letting it melt slightly into the mixture to form a creamy coating.
Gently fold in the roasted squash cubes. Toss everything to coat without breaking up the squash.
Transfer mixture to prepared casserole dish.
In a small bowl, mix panko, melted butter, remaining chopped sage, and Parmesan. Sprinkle over the top.
Bake uncovered for 15–20 minutes, until the topping is golden and crispy.
Let cool slightly before serving.
Notes
To make it more festive: fold in ¼ cup dried cranberries or top with toasted pecans before baking. For extra flair, add pomegranate seeds just before serving.