Preheat the oven to 375°F (190°C).

Bring a large pot of salted water to a boil. Cook lasagna noodles according to the package directions until al dente. Drain and lay flat on a sheet of parchment or a lightly oiled tray so they don’t stick.

Heat olive oil in a saucepan over medium heat. Add the chopped onion and minced garlic. Sauté until soft and translucent, about 3–4 minutes. Let cool slightly.

In a mixing bowl, combine pumpkin purée, ricotta cheese, 1 cup of the shredded mozzarella, salt, black pepper, nutmeg, and Italian seasoning. Stir in the sautéed onion and garlic. Mix until smooth and well combined.

Spread a thin layer of the pumpkin mixture across the bottom of a 9x13-inch baking dish (this prevents sticking).

Place 4 lasagna noodles over the pumpkin base. Spread half of the pumpkin-ricotta mixture over the noodles. Evenly distribute half of the fresh spinach on top, then sprinkle with some Parmesan.

Add another layer of 4 noodles. Spread the remaining pumpkin mixture, then the remaining spinach, and another sprinkle of Parmesan.

Top with the final 4 noodles. Spread the remaining mozzarella over the top and finish with the remaining Parmesan.

Cover the dish tightly with aluminum foil and bake for 30 minutes. Remove the foil and bake an additional 15 minutes, until cheese is bubbly and golden.

Let the lasagna cool for about 10 minutes to set before slicing and serving.