Preheat oven to 375°.
Heat oil in a large nonstick skillet over medium-high heat. Add onion and bell peppers, and sauté 5 minutes. Add mushrooms and garlic; sauté 2 minutes. Stir in basil, salt, black pepper, tomatoes, and tomato sauce, and bring to a boil. Reduce heat; simmer 5 minutes or until slightly thick. Stir in spinach; cook 1 minute or until spinach wilts. Stir in pasta. Spoon into a 13 x 9-inch baking dish coated with cooking spray. Dollop with ricotta.
Cover and bake at 375° for 20 minutes. Uncover; sprinkle with Parmesan. Bake an additional 5 minutes or until lightly browned.
Note: To make ahead, assemble casserole as directed. Cover and refrigerate overnight. Let stand 30 minutes at room temperature, and bake as directed.