Heat grill to medium heat. Lightly spray four rectangles of foil with cooking spray. Set aside.
Place potatoes in a large bowl. Drizzle on olive oil. Sprinkle on ranch seasoning, salt and pepper. Toss to coat potatoes. Place potatoes in center of each of four foil rectangles dividing equally. Fold foil and seal ends. Place on grill seam side down for 10 minutes. Turn pack over and continue to cook for 10 minutes.
Remove packets from grill and carefully open. Sprinkle cheese on top of potatoes and place packet back on grill, closing lid, for 3-4 minutes, until cheese is melted. Top with addition salt and pepper if desired.
Heat oven to 400 degrees. Prepare potato foil packs as instructed above. Cook in oven seam side down for 10 minutes then turn and continue to cook 15 more minutes until potatoes are done. Remove packets from oven, open and sprinkle on cheese. Return to oven for 2-3 minutes until cheese is melted.