1. Cook pasta according to package directions, omitting salt and fat; drain.
2. Preheat oven to 400°.
3. Heat a large skillet over medium-high heat. Add oil to pan. Add squash, zucchini, and onion; sauté 5 minutes. Add tomato and garlic; sauté 3 minutes. Remove from heat; stir in pasta, 1/2 cup mozzarella, herbs, 1/2 teaspoon salt, and pepper.
4. Combine ricotta, remaining salt, and egg. Stir into pasta mixture. Spoon into an 8-inch square glass or ceramic baking dish coated with cooking spray; sprinkle with remaining mozzarella. Bake at 400° for 15 minutes or until bubbly and browned.