Spaghetti Squash with shells

1 medium spaghetti squash (about 3 lbs) 1 cup (or more) sliced fresh mushrooms 1 small onion , peeled and chopped 2 garlic cloves, peeled and minced 1 26-oz.[...]

2 small spaghetti squash (1 1/4 to 1 1/2 pounds) 4 ounces mozzarella cheese , cut into small cubes (1 cup) 3 medium tomatoes , seeded and chopped (1 1/2 cups)[...]