Preheat your oven to 400°F (200°C).

Toss the cubed butternut squash with olive oil, salt, and black pepper. Spread on a baking sheet and roast for 25-30 minutes until soft and caramelized. Blend the roasted squash in a food processor or blender until smooth. Set aside.

In a large skillet, add olive oil over medium-low heat. Add sliced onions and cook for about 30-40 minutes, stirring occasionally, until golden brown. Add the mushrooms, salt, and pepper. Cook for another 5-7 minutes until the mushrooms are tender. Set aside.

In a medium bowl, mix ricotta, Parmesan, mozzarella cheese, chili flakes, grated garlic, wilted spinach, parsley, salt, and pepper. Stir until well combined and smooth.

Preheat your oven to 375°F (190°C). Spread a thin layer of the butternut squash puree at the bottom of a greased 9×13-inch baking dish. Layer 4-5 lasagna noodles over the squash. Spread half of the ricotta mixture, followed by half of the caramelized onions and mushrooms. Then add the mozzarella and parmesan cheese. Repeat the layers: butternut squash puree, noodles, ricotta mixture, onions & mushrooms, and cheeses. Top with the remaining noodles and spread any leftover squash puree on top. Sprinkle mozzarella and Parmesan cheese over the top.

Cover the dish with aluminum foil and bake for 30 minutes. Remove the foil and bake for another 15-20 minutes, until the cheese is golden and bubbly. Let the lasagna rest for 10 minutes before slicing and serving.