Preheat your oven to 400°F (200°C). Toss the peeled and cubed butternut squash with a drizzle of olive oil, salt, and pepper. Spread the cubes evenly on a baking sheet and roast for about 20-25 minutes until tender and caramelized at the edges.
While the squash roasts, bring a large pot of salted water to a boil. Add the lasagna noodles and cook according to package instructions until just al dente. Drain and lay them flat on a clean kitchen towel or parchment paper to prevent sticking.
In a large bowl, combine the roasted butternut squash (mashed or pulsed if desired), fresh spinach, ricotta cheese, half of the mozzarella, Parmesan cheese, egg, garlic powder, onion powder, salt, and pepper. Mix until well incorporated.
Spread a thin layer of marinara sauce on the bottom of your baking dish. Lay a lasagna noodle flat and spoon about 2-3 tablespoons of the filling along one edge. Carefully roll the noodle up and place seam side down in the dish. Repeat with remaining noodles and filling.
Pour the remaining marinara sauce evenly over the rollups. Sprinkle the remaining mozzarella cheese over the top.
Cover the dish with aluminum foil and bake at 375°F (190°C) for 25-30 minutes. Remove foil and bake for another 10 minutes until cheese is bubbly and slightly browned.
Let the rollups rest for 5 minutes before serving. Drizzle a little olive oil on top if desired and serve with your favorite side.