Heat gas or charcoal grill. Cut four 18x12-inch sheets of heavy-duty foil; spray foil with cooking spray.
For each packet, place about 1 cup potato wedges and 3 thigh halves onto center of foil sheet. Drizzle with scant 1/3 cup dressing. Wrap each packet securely using double-fold seals, allowing room for heat expansion.
When grill is heated, place foil packets, seam side up, on gas grill over medium heat or on charcoal grill over medium coals; cover grill. Cook 45 to 50 minutes or until juice of chicken is clear when center of thickest part is cut (180°F) and potatoes are tender.
Open packets carefully to allow steam to escape. Sprinkle each with bacon, onions and pepper.