Set pot to STOVETOP HIGH. Add sausage to pot. Cook uncovered for 10 minutes or until browned, stirring often. Remove sausage from pot. Spoon off fat.
Pour water into pot. Place roasting rack into pot. Place squash, cut side down, on rack. Set OVEN to 425 degrees F for 25 minutes.
Using fork, scrape flesh from squash and add to pot. Sprinkle with 1 tablespoon Parmesan cheese and 1 teaspoon garlic and herb seasoning. Top with sausage, tomato, spinach and remaining Parmesan cheese and seasoning. Set OVEN to 425 degrees F for 15 minutes. Cover and cook until mixture is hot and bubbling. Sprinkle with mozzarella cheese.