1. Immerse cedar planks in water, placing weight on top of each plank to keep it submerged. Soak 4 hours.
2. Heat grill to medium heat. Remove planks from water; brush tops of planks with oil. Place 2 chicken breasts on each plank. Place on grate of grill; cover with lid.
3. Grill 30 min. Meanwhile, mix remaining ingredients until blended.
4. Reserve 1/2 cup dressing mixture to serve with the cooked chicken. Brush chicken evenly with half the remaining dressing mixture. Grill 30 to 45 min. or until chicken is done (165ºF), brushing occasionally with remaining dressing mixture.
5. Remove chicken from grill; discard planks. Remove and discard bones from chicken. Cut each breast in half. Serve with the reserved dressing mixture.