1. Preheat oven to 375ºF. Bring a large pot of salted water to a boil and cook pasta until al dente, about 10 minutes.
2. In a large skillet, warm oil over medium-high heat. Add onion and cook for 2 minutes, stirring. Add bell pepper, squash, zucchini and garlic; sauté for 7 minutes. Remove from heat. Season with salt and pepper.
3. Drain pasta and return to pot. Add spaghetti sauce, vegetable mixture and basil; stir. Taste and season with salt and pepper. In a small bowl, mix together ricotta, 1 1/2 cups mozzarella and 1/4 cup Parmesan.
4. Mist a 9-by-13-inch baking dish with cooking spray. Spread half of pasta mixture in dish; drop spoonfuls of ricotta mixture over pasta. Cover with remaining pasta. Sprinkle with remaining mozzarella and Parmesan. Bake until bubbling, about 35 minutes. Allow to rest for 10 minutes before serving.