MIX 1 cup of the barbecue sauce, the lime juice and water until well blended; set aside. Score both sides of steak by making shallow cuts in surface. Place steak in glass dish. Pour barbecue sauce mixture over steak; cover. Refrigerate several hours or overnight to marinate. Drain; discard marinade.
PREHEAT greased grill to medium heat. Grill steak, peppers and onions 12 to 14 min. or until steak is cooked to medium doneness (160°F) and vegetables are crisp-tender, turning and brushing occasionally with the remaining 1/4 cup barbecue sauce.
CUT steak across the grain into thin slices. Coarsely chop vegetables. Spoon steak and vegetables evenly onto tortillas; roll up.