Drain the oysters and place in a small bowl. Cover with 240ml milk and let soak for 15 minutes. In a medium bowl, whisk together remaining milk, water, cayenne and eggs. Place the flour, cornmeal, black pepper, and salt into a brown paper bag, close and shake to mix.
In a large heavy-bottomed pot, pour enough oil to fill the pan halfway. Heat until a deep-frying thermometer inserted in the oil reaches 180°C.
Drain the oysters from the milk. In batches dip oysters in the egg mixture then drop in the paper bag. Close and shake. Remove to a plate and repeat with the rest of the oysters. When oil is at 180°C, fry oysters in batches. Do not overcrowd. Cook turning once until golden brown and cooked through, about three minutes. Remove to a paper towel. Repeat with remaining oysters.
To serve, cut sandwich loaves in half horizontally. Slather a generous amount of Spicy Remoulade Sauce on the inside. Place a lettuce leaf inside and fill generously with oysters. Squeeze fresh lemon juice over oysters just before serving.
For the spicy remoulade sauce: Place all ingredients into a food processor and blend until smooth. Chill until ready to serve. Makes 350ml.