Step 1: Prepare the Dill Pickle Tartar Sauce: In a small bowl, combine mayonnaise, chopped dill pickles, fresh chopped dill, fresh lemon juice, Dijon mustard, and salt and black pepper to taste. Stir until well combined. Cover and refrigerate for at least 30 minutes to allow flavors to meld. This can be made a day ahead.
Step 2: Prepare the Fish: Pat fish fillets thoroughly dry with paper towels. Season both sides generously with salt and black pepper.
Step 3: Set up Breading Station: Place flour in one shallow dish, whisked eggs with milk/water in a second, and panko breadcrumbs in a third.
Step 4: Bread the Fish: Dredge each fish fillet first in flour, shaking off excess. Dip into egg mixture, ensuring full coating. Finally, press into panko breadcrumbs, coating thoroughly on all sides. Gently press panko onto the fish.
Step 5: Heat Oil: Heat 1-inch of vegetable oil in a large skillet over medium-high heat to 350-375°F (175-190°C).
Step 6: Fry the Fish: Carefully place 1-2 breaded fish fillets into the hot oil, ensuring not to overcrowd. Fry for 3-4 minutes per side, or until golden brown and cooked through (fish should flake easily).
Step 7: Drain Fish: Remove fried fish from oil and place on a wire rack set over a baking sheet lined with paper towels to drain excess oil. Immediately sprinkle with a little extra salt. Repeat with remaining fillets.
Step 8: Assemble Sandwiches: Lightly toast buns. Spread a generous amount of dill pickle tartar sauce on both halves of each bun. Place a crispy fried fish fillet on the bottom bun. Top with lettuce, tomato slices, and extra dill pickle slices if desired. Close with the top bun and serve immediately.