Heat the oil to 350 degrees F in a large 12- or 14-inch cast-iron skillet filled halfway up.
Mix the flour, paprika and garlic salt in a bowl. Add the beer and whisk until the mixture reaches the consistency of a thin pancake batter. Rest the batter in the fridge for 15 minutes.
Once rested, dunk the fish in the batter, let excess drip off and then gently slide the fish into the oil. Fry until just golden brown, about 3 minutes. Remove the fish to a wire rack set over a sheet tray and season with salt.
The sandwich build: Lay a piece of American cheese on each bun, set a piece fish on top, then dollop on an even layer of Chipotle Tartar Sauce and sprinkle with red onion.
In a bowl, combine the mayonnaise, relish, honey, mustard, chipotle and a little hit of the adobo sauce. Season with salt and pepper, and then prepare to want to put this sauce on everything.