Prepare Tartar Sauce : In a small bowl, combine mayonnaise, dill pickle relish, lemon juice, Dijon mustard, and capers (if using). Season with salt and pepper to taste. Cover and refrigerate until ready to serve.
Prepare Fish Fillets : Pat fish dry with paper towels and season with salt and black pepper.
Set Up Breading Station : Place flour in one shallow dish. Beat eggs in a second dish. Mix panko breadcrumbs with paprika and garlic powder in a third dish.
Bread the Fish : Dredge each fillet in flour, shaking off excess. Dip in beaten eggs, then coat thoroughly with panko mixture.
Cook the Fish : Heat vegetable oil in a large skillet over medium-high heat. Fry fish fillets 3–4 minutes per side, or until golden brown and cooked through (internal temp 145°F / 63°C). Drain on paper towels.
Prepare Sandwich Components : Toast buns lightly. Slice tomato and prepare lettuce leaves.
Assemble Sandwich : Spread tartar sauce on top and bottom buns. Place lettuce on the bottom bun, then tomato, crispy fish, and additional tartar sauce if desired. Cover with top bun and serve immediately.