1To make marinade, in shallow glass or plastic dish, or resealable food-storage plastic bag, mix all ingredients except chicken.
2Between pieces of plastic wrap or waxed paper, place each chicken breast smooth side down; gently pound with flat side of meat mallet or rolling pin until about 1/4 inch thick. Add chicken to marinade; turn to coat. Cover dish or seal bag; refrigerate at least 30 minutes but no longer than 24 hours.
3Heat coals or gas grill for direct heat. Remove chicken from marinade; discard marinade. Cover and grill chicken over medium heat 8 to 10 minutes, turning once, until juice of chicken is clear when center of thickest part is cut (170°F).