Prepare grill to medium-high heat. Sprinkle turkey breast evenly with 1/2 teaspoon of salt and 1/2 teaspoon of pepper. Place turkey, breast-side down, on prepared grill. Cook to a golden brown, turning to sear all sides, about 15 minutes. Meanwhile, in a small bowl, combine barbecue sauce, vinegar, brown sugar, mustard, Worcestershire sauce, remaining 1/4 teaspoon salt and remaining 1/4 teaspoon pepper; mix well. Baste entire surface of turkey with sauce. Combine grilling, allowing surface to caramelize and turn deep golden brown, but without burning, about 15 minutes. Remove breast from the grill and wrap in aluminum foil, sealing all sides. Return to grill until turkey has reached an internal temperature of 170ºF. to 175ºF. about 45 minutes. Remove from grill and let sit for 10 minutes before carving.