Spaghetti Squash with onion

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)[...]

1 small spaghetti squash halved and seeded * 1/2 tablespoon olive oil or any vegetable oil 1 each onion finely chopped 4 cloves garlic or to taste, minced 2[...]