Begin by drying the cod fillets with paper towels, seasoning them with salt and black pepper.
Allow the fish to sit while you prepare the other components.
In one shallow bowl, whisk together the egg with paprika.
In another bowl, combine flour and the remaining salt and pepper.
Prepare a third bowl with panko bread crumbs.
Dip each fish fillet first in the flour mixture, then into the egg, and finally roll it in panko to coat evenly.
Make sure every fillet is well-coated for maximum crunch.
Heat vegetable oil in a frying pan over medium heat until it shimmers.
Fry the fish pieces for 3-4 minutes per side until golden brown and crispy.
Remove and drain them on paper towels.
Mix mayonnaise, pickle relish, and lemon juice in a small bowl to create the tartar sauce.
Spread the sauce on both sides of each bun.
Add a slice of American cheese.
Top with crispy fish.
Serve immediately.