In a large pot over medium heat, heat oil. Add onions, bell peppers, tomatoes, and squashes. Cook until softened, about 5 minutes. Add garlic and cook until fragrant, about 1 minute more.
Add pasta, water, half-and-half, oregano, salt, pepper, and red pepper flakes and season with salt and pepper. Bring to a boil, and cook for 15 minutes. Add shrimp and cook until shrimp is opaque and pasta is al dente, 3 to 5 minutes more. Stir in Parmesan.
Top with basil before serving.
