In a large heavy-bottomed saucepan, pour enough oil to fill the pan about a third of the way. Heat over medium heat until a deep-frying thermometer inserted in the oil reaches 360 degrees F.
Place the flour in a small shallow mixing bowl or pie plate. Add the garlic powder, onion powder, paprika, black pepper, salt and cayenne, and stir to combine. Place the beaten eggs in another bowl, and place the panko in a third bowl.
Dredge a fillet in the flour, then dip in the eggs and finish with a coating of panko. Repeat for the remaining fillets. Place the fillets in the oil and fry until golden, 4 to 6 minutes.
Place each fillet on a roll. Top each with 1/2 cup shredded lettuce and some pickle slices. Finish with 2 tablespoons Homemade Tartar Sauce or serve it alongside.
Place the mayonnaise, chives, cornichons, parsley, capers, lemon juice, salt and pepper in the bowl of a food processor or mini chopper fitted with a steel blade, and pulse until the pickles are finely chopped and all the ingredients are mixed but not pureed.