Combine the first three ingredients in a large dish. Add chicken, tossing to coat. Cover and marinate in refrigerator for 30 minutes to 1 hour. Cut carrot and celery lengthwise into 12 thin strips using a vegetable peeler. Place strips in a bowl of ice water. Let stand 30 minutes. Place potato in a saucepan; cover with water. Bring to a boil; cook 15 minutes or until tender. Drain and cool.
Prepare grill. Remove chicken from grill and discard marinade. Place chicken on grill rack coated with cooking spray. Grill 5 minutes on each side or until the chicken is done. Cut chicken diagonally across the grain into slices. Set aside. Arrange lettuce on a large platter. Top with potato, carrot and celery strips, chicken and tomato halves. Serve with Blue Cheese-Buttermilk Dressing.
