Combine the buttermilk and 2 teaspoons of hot sauce in a small bowl. Add the oysters and refrigerate for 30 minutes to an hour.
While the oysters are soaking, whisk the mayonnaise, lemon juice, mustard, the remaining tablespoon of hot sauce, pickle brine, 1/2 teaspoon of kosher salt, parsley, black pepper, cayenne, garlic powder and sumac together in a medium mixing bowl. Add the iceberg lettuce and toss to coat. Cover and refrigerate for 30 minutes.
Heat the peanut oil in a 5-quart Dutch oven over high heat until it reaches 350 degrees F on a deep-fry thermometer. Then lower the heat to slowly bring the oil up to 375 degrees F.
Meanwhile, combine the cornmeal, panko, the remaining 1 1/2 teaspoons of salt and nutmeg in a medium bowl
Remove each oyster from the marinade and shake off the excess moisture. Dredge in the cornmeal mixture, then move to a cooling rack set over a half-sheet pan. Allow the oysters to sit for several minutes afterwards to allow the breading to set.
Transfer 6 oysters at a time to the hot oil and fry until golden brown, 1 1/2 to 2 minutes. (Watch your thermometer because the introduction of cold food will likely pull the temperature down a bit.)
Carefully transport the fried oysters to a clean cooling rack. Sprinkle with freshly ground black pepper. Bring the oil back to 370 to 375 degrees F and repeat with the remaining oysters.
Split the rolls in half lengthwise. Tear out a bit of bread from the center of each roll, creating a trough. (If you wish, lightly toast the rolls in a 375 degrees F oven for 3 minutes.)
Line the bottom of your roll with slaw and top with 5 to 6 oysters.
Consume. Notice how the slaw is kind of gooshy (in a good way) and how that contrasts with the crunch of the oysters. Pulling some of the bread out of the middle will help the sandwich stay together, but you're still going to need a roll of paper towels to eat this thing.