Shuck the oysters and then place the prawns, oysters and cooked beef, if using cooked, into bowls. Divide the rub ingredients evenly between the bowls. If cooking the beef from fresh, rub over the beef before cooking.
Coat them all over in the rub ingredients.
Place the buttermilk and flour into separate bowls. Then coat the shrimp and the oysters, starting with the buttermilk and then the flour. Make sure they are well coated.
Deep fry both in frying oil at 180 for a few minutes. until crisp and golden.
Divide the mayo into two small bowls, one with 2 tablespoons the rest in the other. To the small one add the Sriracha and add the remaining ingredients to the other to make a tartare sauce.
Half the rolls lengthwise and add the tartare sauce to the two, the spicy mayo to the other. Layer in the lettuce and tomatoes and add the fish and meat to the paired rolls. Serve with any extra sauces if you fancy.