With a fork, stab the flank steak all over to perforate it full of tiny holes. Place in a zip-top plastic bag.
In a small bowl, stir together the lime juice, half of the olive oil (reserve the rest - you'll be needing it in a minute), the oregano, garlic, cumin and black pepper. Pour half of this marinade (half! only!) into the bag with the meat. Press as much air out of the bag as possible and seal shut. Refrigerate and allow to marinate for at least 4 hours or overnight.
Into the remaining marinade, stir the reserved olive oil, the sugar and the salt. Set aside - this will be the salad dressing.
Preheat the barbecue grill to high. Remove beef from marinade and place on the preheated grill (discard marinade). Grill the steak, turning once or twice, until done the way you like it. Remove to a plate, let cool, then with a very sharp knife, slice as thinly as possible against the grain. Transfer to a large bowl. Add the corn, kidney beans, red onion and jalapeno pepper. Drizzle with about half of the reserved dressing, toss to combine and refrigerate for about an hour before serving.
At serving time, arrange the lettuce on a large platter. Top with the steak mixture, the diced tomato and the shredded cheese. Drizzle with the remaining dressing, and serve with tortilla chips crumbled on top.
Sorry, there is no nutrition information available for this recipe.