1. Whisk together egg and buttermilk in a large bowl. Stir together cornmeal, flour, and seasoning in a large plastic bag. Dredge shrimp and oysters, in batches, in egg mixture, and then add to cornmeal mixture, shaking to coat well.
2. Pour oil to a depth of 2 inches in a deep heavy pot or Dutch oven; heat over medium-high heat until temperature reaches 350° to 375°.
3. Fry shrimp and oysters, in batches, 1 to 2 minutes or until golden brown and just cooked through. Drain on paper towels.
4. Spread insides of baguettes with Tartar Sauce, and top with lettuce, tomatoes, shrimp, and oysters. Serve with hot sauce and additional Tartar Sauce.