Create the marinade for your flank steak. In a small bowl, combine together the olive oil, lime juice, cumin, chili powder, onion powder, worcestershire, and minced garlic. Put your flank steak strips in and let marinate in the fridge for at least 30 minutes.
Heat a large skillet over high heat. If using your grill, do the same but use a grill safe skillet. In a large bowl, toss together your onion, bell peppers, salt, cumin, chili powder, and red pepper flakes. Saute until the vegetables are tender crisp (7-10 minutes). Remove the vegetables from the pan and transfer to a serving bowl, but keep the skillet hot.
Return the skillet to high heat. Cook your flank steak in it for about 2-3 minutes, stirring throughout. If you are doing this on a grill the flames will jump up and lick the meat so watch your hands and face.
Compile your burgers on the bun with (optional) 1 slice of pepperjack cheese on bottom, flank steak, another slice of pepperjack (optional), a heaping pile of peppers, a handful of cilantro leaves, and a dollop of sour cream. Toast the buns for an extra nice touch.