Prepare the ingredients for the recipe. When purchasing oysters, have the store open them up for you. If doing it yourself, pull oyster shells apart using an oyster knife. Discard the top shell and loosen the oyster meat using the tip of the oyster knife.
Leave the oysters inside the bottom shells and place them directly over the coals or the grill rack, facing upward; grill for approximately 3 minutes. Top each oyster with about 1/2 teaspoon of the miso butter mixture; use a bit more for larger oysters and less for smaller ones.