Place meatballs on microwavable plate. Microwave on High 2 to 3 minutes or until meatballs are hot.
Meanwhile, in medium skillet, heat oil over medium-high heat until hot. Add mushrooms, bell pepper and onion; cook 4 to 5 minutes, stirring frequently, until vegetables are tender.
Add pasta sauce and meatballs; mix well. Cook, stirring occasionally, until thoroughly heated.
Spoon 5 meatballs and half of sauce into each hoagie bun. Sprinkle with cheese.