Cook pasta according to package directions, drain – set aside. In a skillet over medium heat, cook sausage with green bell pepper and onion until sausage is evenly cooked, drain. In another skillet over medium-low heat, combine tomatoes, tomato sauce, garlic powder, salt, and oregano. Preheat oven to 350 degrees. Using a 3 quart baking dish, layer ziti, sausage, mozzarella cheese, and sauce. Repeat layers, and top with Parmesan cheese. Bake in the preheated oven 45 minutes, or until top is golden brown.