Preheat oven to 350°F. Lightly grease a 9x13 baking dish.
Cook pasta according to directions.
In a large skillet, cook ground turkey and onion over medium heat until turkey is no longer pink. Drain fat. Sprinkle with salt and pepper.
In a large bowl, combine mozzarella, ricotta, egg, Parmesan, and Italian seasoning. mIx well. Stir in pasta.
Pour pasta mixture into prepared baking dish. Top with meat mixture and spaghetti sauce. Cover with foil. Bake at 350°F for 45 minutes. Remove foil, sprinkle mozzarella cheese on top of casserole and bake an additional 15 minutes or until cheese is melted.