01 - Preheat oven to 400°F or heat 1/2 inch of oil in a large skillet over medium-high heat for shallow frying.
02 - Pat fish pieces dry with paper towels, then season both sides generously with salt and black pepper.
03 - Prepare three shallow bowls: place flour in the first, beaten eggs in the second, and mix panko breadcrumbs with cornmeal in the third.
04 - Dredge each fish piece in flour, shaking off excess. Dip into egg mixture, allowing excess to drip off. Press firmly into panko-cornmeal mixture to coat completely on all sides.
05 - For frying: cook fish in batches for 2-3 minutes per side until golden brown and cooked through. For baking: arrange on a parchment-lined baking sheet and bake for 10-12 minutes, flipping once halfway through.
06 - Combine mayonnaise, chopped pickles, capers, lemon juice, Dijon mustard, and fresh parsley in a mixing bowl. Refrigerate until ready to serve.
07 - Lightly toast slider buns in a dry skillet or under the broiler for 1-2 minutes until golden.
08 - Place a cooked fish fillet on the bottom half of each bun. Top with a slice of cheese, lettuce, and a generous spoonful of tartar sauce. Cover with bun tops and serve immediately.