Preheat oven to 375°F (190°C) if baking the sausage, or heat a skillet over medium heat if pan-frying.
Cook the Italian sausages until no longer pink inside, either by baking or pan-frying; drain any fat, let cool slightly, then halve each sausage lengthwise and slice into 1/2-inch pieces.
Heat 2 tablespoons of the olive oil in a skillet over medium heat and sauté the chopped green bell pepper until it loses its crispness but is not fully soft, about 4–6 minutes; set aside.
In a heavy saucepan, combine the canned tomatoes (crushed by hand for a chunky texture), tomato puree, minced garlic, 4 tablespoons of olive oil, and the fresh basil; bring to a light simmer over medium heat.
Add the sautéed peppers and sliced cooked sausage to the sauce and simmer together for 3–5 minutes to meld flavors; season with salt and pepper to taste.
Meanwhile, cook the ziti in a large pot of salted boiling water according to package directions; reserve 1/2 cup pasta cooking water if needed, then drain the pasta.
Toss the drained pasta with the marinara sauce and, if needed, a little reserved pasta water to help the sauce cling; plate the pasta and top with the sausage, peppers, and tomato-basil sauce.
Garnish each serving with chopped parsley and grated Parmesan cheese before serving.
