Prepare the fish batter mix according to package directions and coat the shrimp in the batter. Marinate the shrimp for up to 1 hour in the refrigerator.
Preheat the oil in a deep fryer to 365 degrees F. Alternatively, fill a cast-iron pot halfway with oil and heat until a deep-frying thermometer inserted in the oil reaches 365 degrees F.
Dredge the shrimp in the cornmeal coating. Shake off any excess cornmeal and fry until light golden brown and crispy, 3 to 4 minutes. Dredge the oysters in the cornmeal coating. Shake off any excess cornmeal and fry until light golden brown and crispy on the outside but soft on the inside, 4 to 5 minutes.
Halve the bread lengthwise. Spread the mayonnaise on the top half of the bread, then add the lettuce, ketchup, pickle slices and some hot sauce. On the bottom half of the bread, place the oysters on one side and the shrimp on the other. Close the two bread halves and slice the sandwich in half to serve.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Domilise's Po-Boys and Bar, New Orleans, LA