Preheat an outdoor grill over medium heat. Slice the potatoes into ¼ inch thick slices. Rinse with water and pat dry. Spray a sheet of aluminum foil with non-stick cooking spray. In a bowl combine the sliced potatoes, ¾ of the ranch dressing, garlic powder, salt, and pepper. Mix well and place the potato mixture into the center of the foil.
Top the potatoes with bacon and cheddar and wrap the foil around the potato mixture to form a packet and seal.
Place onto the grill and cook for 20-25 minutes with the lid closed. Flip once through the process about ¾ of the way through cooking. Remove from the grill and let sit 5 minutes. Spoon the remaining ranch dressing over the top of the potatoes for serving and garnish with fresh parsley.