To make the Spicy Tartar Sauce: Mix all the sauce ingredients in a small bowl until well combined. Cover and refrigerate until ready to serve.
In a deep 12-inch pan set over medium-high heat, add enough oil so it comes 1/3 of the way up the sides. Heat the oil to 375 degrees F.
In a wide-mouth bowl, whisk the eggs with the hot sauce, seafood seasoning and a pinch of salt. In a small paper bag, mix together the cornmeal, flour, cornstarch, and salt and pepper, to taste. Dredge the catfish in egg mixture, then in the flour mixture. Gently shake off excess flour. Set aside and repeat with remaining flounder. Fry the fish in batches until golden, about 2 to 3 minutes each side, being careful to keep the temperature at 375 degrees F. Remove catfish to a paper towel to drain and immediately season with salt.
Slice the sandwich rolls in half, slather the cut sides with butter and season with salt. Arrange, cut side up, on a baking sheet and toast in the oven until lightly golden, about 8 minutes. An alternate is to put them, buttered side down, on a griddle or under a broiler, and toast until golden. Set aside.
To assemble sandwiches, slather the rolls with the Spicy Tartar Sauce, top with lettuce and catfish, and serve.