Preheat outdoor grill to medium-high heat according to manufacturer's directions. Place four 18x2-inch pieces of heavy foil on counter. Spray each with cooking spray. For each packet, spread a generous teaspoon barbecue sauce in center. Place 1/2 cup potatoes in single layer over sauce. Spoon another teaspoon sauce over potatoes.
Top potatoes with chicken. Spoon 1 teaspoon sauce over each breast. Top each with 1/4th bell pepper, onion and black pepper. Bring up short sides of each foil packet and double fold top. Double fold both ends to seal each packet, leaving space for steam to gather.
Place packets on grate of covered grill. Gril 15 to 20 minutes or until chicken is no longer pink in centers (165°F) and potatoes are tender. Carefully open packets; sprinkle 1/4th cheese on top of each breast. Close foil and let stand 2 minutes or until cheese melts.
Packets may be baked in shallow pan in 425°F oven 20 minutes or until chicken is no longer pink in centers and potatoes are tender.