Place the oysters directly on the grill or on a baking sheet or cast iron pan layered with rock salt to keep them stable. Cover the grill and cook for 1 minute to slightly open them. Carefully remove, and wearing oven mitts, shuck the oysters, keeping as much oyster liquor as possible. Place 2 teaspoons of garlic parsley butter on each oyster, then place back on the baking sheet or cast iron pan, cover the grill and cook for 3 minutes. Carefully remove the oysters and place on a seaweed or rock salt lined platter.