Rinse lentils until the water runs clear.

Combine lentils and water in a medium saucepan. Bring to a boil over high heat, skimming off any foam that rises to the top.

Reduce heat to low, partially cover, and simmer, stirring occasionally, until the lentils are soft and beginning to break down, 20 to 25 minutes. The mixture should look creamy and thick.

While the lentils cook, heat avocado oil in a medium skillet over medium heat. Add cumin seeds and cook until sizzling and fragrant, about 30 seconds.

Stir in onion and cook until soft and translucent, 5 to 6 minutes.

Add garlic and ginger; cook until fragrant, about 30 seconds.

Add coriander, turmeric, and chili flakes. Stir constantly for 1 minute to bloom the spices and deepen their flavor.

Stir in tomatoes and salt. Cook for 2 to 3 minutes, stirring occasionally, until the mixture reduces slightly and the tomatoes soften.

Stir a ladleful of cooked lentils into the tomato mixture to deglaze the skillet.

Pour the mixture back into the pot of lentils. Stir well and simmer together for 5 minutes, allowing the flavors to meld.

Stir in spinach and cook until just wilted and bright green, 2 to 3 minutes.

Remove from heat. Stir in lemon juice and garam masala.

Garnish with chopped cilantro. Serve hot with basmati rice or warm flatbread.