In a large skillet add the Italian sausage, onions, green pepper, and garlic. Cook over medium heat until the sausage is browned and onions, peppers, and garlic are tender.
While the sausage is being prepared, cook the ziti following the instructions on the box. Cook a minute or two less than the package states, so it is al dente.
Once the sausage is browned stir in the spaghetti sauce and diced tomatoes. Add the cottage cheese, 1 cup mozzarella cheese, Parmesan cheese and mix until well combined.
Drain the pasta and set aside.
Spread 1/3 of the meat sauce in the bottom of a 9 by 13-inch pan. Top with half of the noodles. Top the noodles with another 1/3 meat sauce, and repeat one more time. Top with the remaining mozzarella cheese.
Bake for 25 to 30 minutes. Serve.