Preheat a skillet or oven as needed and cook the Italian sausages until fully cooked through. Drain any fat and 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. Add the chopped green bell pepper and sauté until they lose their raw crunch but are not mushy, about 4–6 minutes. Remove and set aside.
In a heavy saucepan, combine the canned tomatoes (crushed by hand for a chunky texture), tomato puree, minced garlic, the remaining 4 tablespoons olive oil, and the fresh basil. Season with salt and pepper to taste.
Bring the sauce to a light simmer over medium heat, then add the sautéed peppers and sliced sausage. Let the mixture simmer together for 3–5 minutes to meld the flavors.
Meanwhile, cook the ziti in a large pot of salted boiling water according to package instructions until al dente. Drain the pasta (reserve up to 1/2 cup pasta water if you need to loosen the sauce).
To serve, plate the cooked ziti and top with the sausage, peppers, and marinara sauce. Sprinkle with chopped parsley and grated Parmesan cheese.