Combine first 5 ingredients in a large shallow dish.
Sprinkle fish with salt; dredge in flour mixture, coating well.
Pour oil to a depth of 3 inches in a Dutch oven; heat to 350°. Fry fish 4 to 5 minutes on each side or until golden brown. Drain on paper towels.
Serve on sandwich buns with cocktail sauce, lettuce, and, if desired, tomato.