1. Heat the oil in a pan.
2. Add the onions and green peppers and saute until tender, about 6-10 minutes.
3. Add the garlic and saute until fragrant, about 30 seconds.
4. Set the onions and peppers aside.
5. Add the steak to the pan and cook until no longer pink, about 3-4 minutes.
6. Mix the vegetables into the steak.
7. Place the steak and vegetables and cheese into the bun and enjoy.
8. (optional) Place the open sandwich, with the cheese on top, under the broiler to melt the cheese.