Preheat oven to 425°F (220°C). Spray a baking sheet with nonstick spray.
Place butternut squash on baking sheet and drizzle with 1 tablespoon olive oil. Season generously with salt and pepper, then stir to coat squash with oil and seasonings.
Roast squash until tender and lightly browned, flipping once (about 30 to 40 minutes).
Meanwhile, heat 2 teaspoons olive oil in a large skillet over medium high heat. Add mushrooms to pan and cook until lightly browned. Season with salt and pepper.
Stir in garlic and pepper flakes; cook until fragrant, about 30 seconds. Then mix in kale, stir well, then add ¼ cup water and cover pan.
Reduce heat to medium low and cook until kale is tender and water is evaporated (about 5 minutes).
Reduce oven heat to 375°F (190°C). Wipe out pan, and set veggies aside until ready to use.
Prepare ricotta:
Mix together ricotta, mozzarella, Parmesan, egg, salt, and pepper. Set aside.
Prepare béchamel:
Melt butter in a large pan over medium heat.
Whisk in flour and cook for 2 minutes, stirring constantly.
Slowly whisk in warm milk. Bring mixture to a boil, then reduce heat to simmer.
Cook until thickened, stirring frequently (about 10 minutes). The sauce should lightly coat the back of a spoon.
Whisk in nutmeg, then season with salt and pepper to taste.
Assemble lasagna:
Spray a 9 x 13-inch pan with nonstick spray.
Spread ¾ cup béchamel sauce over bottom of pan, then top with 3 lasagna noodles.
Cover noodles with ½ of the ricotta. Top ricotta with ½ of the vegetables, then ¾ cup béchamel sauce.
Add another layer of noodles, the remaining ricotta, then the remaining vegetables. Top with ¾ cup béchamel sauce.
Top sauce with remaining 3 noodles, followed by the rest of the béchamel sauce. Sprinkle with 1 cup mozzarella cheese.
Cover lasagna tightly with foil, then bake at 375°F (190°C) for 45 minutes or until hot and bubbly.
Remove foil and bake lasagna until cheese is lightly browned, about 15 minutes.
Let lasagna stand for 5 minutes, then cut into pieces and serve hot. Enjoy!