Boil the Pasta: Bring a large pot of salted water to a boil. Add the rigatoni pasta and cook according to package instructions until al dente.

Sauté the Onion: Heat olive oil in a skillet over medium heat. Sauté yellow onion and crushed red pepper flakes for about 10 minutes until soft.

Brown the Sausage: Add Italian sausage to the skillet, breaking it up as it cooks. Brown for around 5-7 minutes until golden and no pink remains.

Add Garlic: Stir in minced garlic and cook for 1 minute, ensuring not to burn it.

Build the Tomato Sauce: Add tomato paste and grape tomatoes to the skillet. Pour in white wine or chicken broth, then season with salt and pepper. Cook for 10 minutes.

Incorporate Zucchini: Add chopped zucchini and stir well, cooking for an additional 5 minutes until tender but still slightly crunchy.

Drain the Pasta: Reserve 1/2 cup of pasta water, then drain rigatoni in a colander. Do not rinse.

Combine Pasta and Sauce: Add drained rigatoni to the sauce, tossing gently. If dry, add reserved pasta water until desired consistency is reached. Stir in fresh basil.

Serve and Garnish: Serve hot, topped with grated Parmesan cheese and extra fresh basil if desired.