The most important step is to get the flank steak cut as thin as possible. The easiest way to do this at home is to cut it when it is still slightly frozen. Use a sharp knife and cut very thin slices of the steak.  

 In a non stick wok (one with a lid is ideal) heat the olive oil. Add the sliced beef, spices and chopped jalapeño and sauté on a medium-high flame for 5-6 minutes, or until the beef gets some color on it. Add 1/2 cup water, lower the flame, cover and cook for 10 minutes, checking occasionally to make sure the beef doesn’t burn. After ten minutes, check to see if the beef is tender, if not, then repeat this step again by adding water, covering and cooking until the beef is tender and is easy to break.  

At this point turn up the flame to medium-high, add the sliced bell pepper and onion and sauté for 3-4 minutes, just until the veggies soften a little. Check for salt and pepper, adjust accordingly and set aside. 

 Spread a little butter on the cut side of each bread roll and place under the broiler in your oven for 2 minutes. Take the rolls out, but keep them on your baking sheet. Spoon in the steak and pepper mixture, top with two slices of cheese per roll, then place under the broiler again for 2-3 minutes, or until the cheese melts.  

Serve warm. Enjoy!