Preheat your oven to 425°F (220°C).

On a large baking sheet, toss the cubed butternut squash with olive oil, salt, pepper, and nutmeg. Spread in a single layer and roast for 25–30 minutes, or until tender and slightly caramelized.

While the squash is roasting, prepare the filling. In a bowl, combine ricotta cheese, half of the mozzarella, Parmesan, chopped spinach, and the egg. Mix until well combined and set aside.

For the sauce, heat the marinara in a pot and add basil and garlic powder. Allow it to simmer for a few minutes to meld the flavors.

Once the squash is done roasting, remove it from the oven and allow it to cool slightly. In a blender, pulse the roasted squash until smooth, adding a bit of water if necessary for a creamy consistency.

In a 9×13-inch baking dish, spread a thin layer of marinara at the bottom. Lay 3 noodles on top, followed by half of the ricotta filling, half of the pureed squash, and a layer of marinara. Repeat the layers.

For the top layer, add the final noodles, cover with the remaining marinara, and sprinkle with extra mozzarella cheese if desired.

Cover the dish with foil and bake for 25 minutes. Then, remove the foil and bake for an additional 15-20 minutes, until the cheese is bubbly and golden.

Let it cool for about 10 minutes before slicing.