In a food processor or blender, process diced tomatoes with garlic and onion until everything is broken down but still a little chunky.
Add diced tomato mixture, tomato paste, tomato sauce and seasonings to a large skillet. Bring to a slow boil and simmer about 15-20 minutes, until sauce is thickened.
Add meatballs to the skillet and heat through. Spoon meatballs and sauce on hoagie rolls and top with sliced mozzarella cheese.
Bake at 350 degrees for about 10 minutes, until cheese is melted and rolls are just slightly crispy.