How to Make It
Melt butter in a small saucepan over medium. Stir in parsley, lemon juice, garlic, and salt. Remove from heat, and place saucepan next to grill to keep butter warm.
Heat grill to medium (about 400°F). Stir together Parmesan and Romano cheeses in a bowl.
Shuck oysters, and discard top shell. Using an oyster knife, disconnect the oyster from the bottom shell, keeping the oyster in the shell. Place the raw oysters on the half shell on the grill, and top each oyster with about 1 tablespoon of the butter mixture. Grill, uncovered, until juices start to bubble and the edges of the oysters begin to curl, about 2 minutes. Top each oyster with a generous pinch of the cheese mixture. Continue grilling, uncovered, until the edges of the shells start to brown, about 2 minutes. Using tongs, transfer oysters from grill to a serving platter. Top with any remaining butter mixture. Serve with grilled or baked French bread.
Note: Large oysters are important here, because they stand up better on the grill and cradle more of the buttery sauce.