For the sauce: Heat 1 tablespoon of the olive oil in a large skillet over medium-high heat. Add the sausage and use a wooden spoon to break up the meat as it browns. When the sausage has cooked to golden brown, about 8 minutes, transfer it to a paper towel-lined plate to drain. Return the skillet to medium heat and add the remaining tablespoon olive oil. Add the onions and use a wooden spoon to scrape up any browned bits left on the bottom of the skillet. Deglaze with 2 tablespoons water. Cook until the onions are translucent, stirring occasionally, about 8 minutes. Add the mushrooms and cook until browned, 4 to 5 minutes. Stir in the garlic and a pinch of crushed red pepper and cook about 2 minutes. Add the sausage back to the skillet. Stir in the canned butternut squash, cream, salt and pepper. Set aside.
For the filling: In a medium bowl, combine the ricotta, Parmesan, kale, sage, garlic powder, salt, pepper, eggs and nutmeg. Stir to combine and set aside.
For the lasagna: Preheat the oven to 400 degrees F. Bring a large pot of salted water to a boil.
Cook the lasagna noodles in the boiling water for half the time the package recommends. Drain and toss with a drizzle of olive oil to prevent them from sticking together.
Spray a 9-by-13-inch casserole dish with nonstick cooking spray. Spoon about a cup of the sauce into the dish, spreading it to cover the bottom. Arrange half the lasagna noodles over the sauce, then begin layering first with half of the ricotta filling, then half of the sauce, then half of the mozzarella. Continue layering with the remaining noodles, filling and sauce, finishing with mozzarella on top. Sprinkle with the Parmesan. Tap the casserole on the counter to force out any air bubbles.
Bake until the cheese is golden brown and the lasagna is bubbling, 35 to 45 minutes. Let it rest for 15 minutes so it can set and be cut easily.