Place chicken on cutting board and use a kitchen mallet, rolling pin or small saucepot to flatten any thick ends. This step ensures even width and even cooking. Pour dressing into a large resealable plastic bag. Place chicken in bag with dressing. Seal bag and refrigerate 30 minutes to 1 hour to marinate.

Preheat barbecue to medium heat. Remove chicken from plastic bag; discard marinade. Place chicken on grill; cover with lid. Grill 6 to 8 minutes on each side or until cooked through. Brush with barbecue sauce during last few minutes of grilling time.