Heat the oil to 365° F in a large sturdy skillet or pot
Lightly season the fish fillets with salt and pepper
Mix the egg and water together.
Place the flour on a plate, the egg mixture in a medium bowl, and the panko in a medium bowl.
Dredge each fillet, starting with the flour, shaking off excess.
Submerge fillet into egg mixture and then shake off excess.
Dredge the fillet into the Panko crumbs, helping the crumbs adhere with your fingers.
For extra crunchy, repeat this entire dredging process.
Place the fillets on a rack until ready to fry (can be kept in the refrigerator for up to 2 hours).
Carefully place the fillets in the hot oil, and fry until golden, about 2 to 3 minutes.
Remove fillets with metal tongs and place on paper towel-lined plate.
Split the buns and lightly toast.
Spread the tartar sauce on the bottom bun, then add the lettuce, two fillets, and top with tomato, pickles and top bun.