Preheat grill to 350° to 400° (medium-high) heat. Cut steak into 1-inch cubes. Thread steak, onion, and tomatoes alternately onto skewers, leaving a 1/4-inch space between pieces. Sprinkle kabobs with Smoky Barbecue Rub.
Grill kabobs, covered with grill lid, 4 to 5 minutes on each side. Serve with White Barbecue Sauce.