In a large mixing bowl, combine diced potatoes, onion and steak.
Pour olive oil over the top and toss until well combined.
Place 4-6 pieces of foil (approx 12 x 18 in) on a clean working space.
Divide steak and potato mixture evenly between foil pieces.
Season with salt and pepper, to taste.
In a small mixing bowl, combine butter, parsley, garlic, salt and pepper.
Divide garlic butter evenly between foil packs and place on top of steak and vegetables.
Fold the ends of the foil together and seal open ends closed tightly.
Place foil packs on the grill and close lid.
Cook for 15 minutes, turning over halfway through, until meat is cooked and vegetables are tender.
Carefully open foil packs and serve.
Notes
Be sure to use high quality aluminum foil so your foil pack is sturdy enough to transport. You can always add a second layer of foil if you are worried about it being too flimsy.