Add the fresh spinach to the skillet and cook until wilted.
Spread a generous layer of marinara sauce on the bottom of a baking dish.
Layer 3 lasagna noodles onto the sauce, then half of the ricotta, half of the squash and spinach mixture, half of the mozzarella, and a sprinkle of Parmesan.
Repeat the layers as before.
Cover the lasagna with foil and bake for 25 minutes.
Remove the foil and bake for an additional 15 minutes until golden and bubbly.
Let the lasagna cool for a few minutes before slicing and serving.
Notes
Feel free to swap spinach for kale or add other veggies like mushrooms. Refrigerate leftovers for up to 3 days.