In a large skillet add the Italian sausage, onions, and garlic. Cook over medium heat until the sausage is browned and the onions are tender.
While the sausage is being prepared, cook the ziti following the instructions on the box.
Once the sausage is browned stir in the spaghetti sauce and diced tomatoes. Add the cottage cheese, 4 ounces mozzarella cheese, Parmesan cheese, and Italian seasoning and mix together.
Drain the pasta and mix into the sausage mixture.
Pour into a 9 by 13-inch baking dish. Sprinkle with the rest of the mozzarella cheese. Place in the oven that has been preheated to 350 degrees F.
Bake for 25 to 35 minutes. Serve.