Sprinkle chicken with pepper; place on an oiled grill rack over medium heat. Grill, covered, until a thermometer reads 165°, 5-7 minutes per side, basting frequently with 1/2 cup barbecue sauce during the last 4 minutes. Cool slightly. Cut into cubes., Divide dough in half. On a well-greased large sheet of heavy-duty foil, press each portion of dough into a 10x8-in. rectangle; brush lightly with oil. Invert dough onto grill rack; peel off foil. Grill, covered, over medium heat until bottom is lightly browned, 1-2 minutes., Remove from grill. Spread grilled sides with remaining barbecue sauce. Top with cheese, chicken and onion. Grill, covered, until bottom is lightly browned and cheese is melted, 2-3 minutes. Sprinkle with cilantro.