Preheat your grill to medium-high heat 425° F.
Tear off four 16" pieces of Reynolds Wrap® Heavy Duty Foil and spray the middle of each piece (where food will touch) with non-stick cooking spray
To a medium-sized prep bowl, add one chicken breast, 4 tablespoons BBQ sauce (a little more is fine if you want them extra saucy), 1/4 of the potatoes, and 1/4 of the onions. Season with salt & pepper and toss everything together. Place the mixture in the middle of the foil then repeat 4x until you've used all the ingredients.
To fold the foil packets, bring up the long sides of the foil so the ends meet over the food. Double fold the ends (leaving room for heat to circulate inside), then double fold the two short ends to seal the packets.
Place the foil packets on the grill and cook for 30 minutes or until the chicken is cooked through (165F) and the potatoes and onions have softened.
Let the packets rest for 1-2 minutes. Open them carefully, as they will be very hot. Serve with fresh parsley sprinkled over top if desired.