Bring a large pot of salted water to a rolling boil over high heat. Once boiling, add the rigatoni pasta, stirring occasionally. Cook until al dente, about 9 to 10 minutes.

In a wide pot over medium heat, warm the olive oil. Add chopped yellow onion and a pinch of crushed red pepper flakes. Sauté for about 10 minutes until the onion is soft and translucent.

Add the Italian sausage to the pot, breaking it apart with a spoon. Allow it to brown for 7 to 8 minutes until there's no pink visible.

Stir in minced garlic and cook for an additional minute until fragrant. Mix in tomato paste and allow it to caramelize for about 2 minutes.

Fold in grape tomatoes and white wine or chicken broth. Season with salt and black pepper. Let it simmer for about 10 minutes, pressing the tomatoes gently to release juices.

Add diced zucchini to the pot and cook for another 5 minutes until tender but still crunchy.

Reserve ½ cup of pasta water before draining the pasta. Add drained rigatoni directly into the sauce, tossing gently to coat. Incorporate reserved pasta water until desired consistency is reached.

Remove from heat and stir in chopped fresh basil. Serve topped with freshly grated Parmesan cheese.