Preheat oven to 350 degrees.

Heat a large pot of well salted water for the pasta. Cook pasta for 8 minutes. Pasta should still be firm. Drain pasta and splash with cold water to stop the cooking.

Add sausage and onion to a large skillet or Dutch oven and heat over medium heat, breaking up the sausage as it cooks. Cook sausage until it is cooked completely with no pink. Drain sausage if needed. Pour sausage and onions into a small bowl and set aside.

Add grated zucchini to the same skillet. Add salt and pepper to taste and cook zucchini until all of the water has cooked out, around 5-6 minutes. Add the sausage and onions back to the skillet. Stir to combine.

Add marinara sauce to the sausage mixture and mix to heat and combine. Add cooked pasta to the skillet and stir to combine.

Prepare a 9x13 casserole dish with either non-stick spray or brush with olive oil. Spoon half the pasta mixture into the dish. Layer a portion of the ricotta, parmesan and mozzarella over the pasta. Cover with the remaining pasta. Layer the rest of the cheese on top.

Place casserole into the preheated oven and cook for 25 minutes. If you want the cheese to be browned in places, place it under the broiler for 3 minutes before removing it from the oven.

Allow Baked Pasta to sit for 5 minutes before cutting and serving.