Gather the ingredients.
Heat a gas or charcoal grill to high heat. Ideally, the grill should hit 500 F. In a small saucepan, gently melt 4 ounces (½ cup) softened unsalted butter . Mix the melted butter with 2 tablespoons finely chopped garlic , 1 teaspoon freshly ground black pepper , and 1 pinch dried oregano . Reserve in a small bowl.
Place 18 large oysters on the half shell right over the hottest part of the grill. The oysters shouldn't be cut loose from the shell as they can slip and fall right through the grill.
Spoon enough of the seasoned butter over the oysters so that some of it will overflow into the fire and flame up a bit. The oysters are ready when they puff up and get curly on the sides, about 5 minutes.
In a small bowl, mix together 1 ounce grated Parmesan cheese and 1 ounce grated Romano cheese . Top the oysters with the cheese mix and 2 teaspoons finely chopped parsley . Serve on the shells immediately.
