Dry the Seafood: Drain the shucked oysters and pat them completely dry with paper towels or a clean kitchen towel to ensure a perfect crust.
Dredge: Combine the flour, salt, white pepper, granulated onion, and granulated garlic in a shallow baking pan large enough to hold the oysters, working in batches if necessary. Coat the oysters evenly in the seasoned flour mixture.
Chill to Adhere: Transfer the coated oysters to a tray lined with parchment paper and refrigerate them for 10 minutes. This short rest helps the coating stick and reduces the chance of it falling off during frying.
Heat the Oil: Pour the neutral oil into a large frying pan. Use a kitchen thermometer to bring the oil to 350°F.
Fry: Fry the oysters in small batches for 1½ to 2 minutes until they turn a deep, golden brown.
Drain: Use a slotted spoon to remove the oysters and drain them in a single layer on paper towels so they stay crisp; never stack them, or they will get soggy.
Prep the Bread: Slice the sub rolls three-quarters of the way down the middle, leaving a working hinge intact. Lightly brush the cut sides with the melted butter.
Toast: Toast the cut sides in a large pan or griddle on medium heat at 350°F until golden brown.
Assemble: Place the toasted rolls on a clean, flat surface. Layer ½ cup of shredded iceberg lettuce at the bottom of each roll and arrange the sliced tomatoes along one side. Divide the crispy oysters evenly onto the rolls.
Sauce and Serve: Drizzle about 2 ounces of remoulade sauce across the top of each sandwich. Garnish each with a lemon wedge and serve immediately alongside potato chips or a fresh ear of buttered corn.