Pat the fish dry and portion into four even ¼-pound filets (about the size and width of the slice of bread).
Add the eggs to a shallow baking dish and sprinkle with salt and pepper. Pulse the crackers in a food processor until they have the texture of fine breadcrumbs and spread out onto a plate.
On a separate plate, spread the panko and season with salt and pepper. Dip the fish pieces in the egg, then into the crackers, back into the egg and finally into the panko. Press firmly at each step so the breading sticks to the fish well.
Grate the onion and pickles on a box grater. Transfer to a strainer and squeeze out the excess moisture. Combine the grated onions and pickles with slaw mix in a large mixing bowl with chopped carpers, mayonnaise, mustard, lemon juice and cayenne. Mix well and season with salt and pepper. Refrigerate, covered until ready to use.
Add 1-inch of oil to a large, heavy skillet set over medium-high heat. Heat the oil to 350 degrees F. Working in batches, fry the fish until cooked through and golden, 3-4 minutes each side. Drain the fish on a wire rack and season with salt.
Brush the King’s Hawaiian Sweet Sliced Bread with garlic butter and toast the bread until golden.
Place two slices of American cheese on each piece of fish and place the fish under the broiler for about 30 seconds to melt the cheese.
To assemble, smear the insides of the bread with tartar slaw and add the fish. Serve with extra slaw on the side.