Place the flank steak in a plastic zipper bag. Pour in the Korean BBQ sauce and rub it around the flank steak. Seal the bag and place the steak in the fridge for at least 24 hours to marinate.
Preheat a grill or cast-iron skillet. Remove the steak from the fridge and allow it to come to room temperature for at least 30 minutes before grilling.
Salt and pepper each side of the flank steak and place the steak on the grill. Grill the steak on each side for about five minutes. Remove the steak from the grill and allow it to rest before slicing.
Once cooled, slice the steak and divide it between the tortillas. Garnish each tortilla with desired toppings!
