Preheat your grill to medium heat, around 375°F (190°C).
In a large mixing bowl, combine the potato slices, olive oil, salt, black pepper, and garlic powder. Toss until the potatoes are evenly coated.
Cut a large piece of aluminum foil and place the potatoes in the center. Fold up the edges to create a sealed packet.
Place the foil packet on the grill grates and cook for about 20-25 minutes, or until the potatoes are tender and golden brown.
Carefully remove the foil packet from the grill using tongs, and allow it to cool slightly before opening.
Garnish with fresh parsley before serving, if desired.