01 - Preheat oven to 400°F or heat 1/2 inch oil in a large skillet over medium-high heat for shallow frying.
02 - Pat fish pieces dry and 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.
05 - For frying: cook fish in batches 2-3 minutes per side until golden brown and internal temperature reaches 145°F. For baking: arrange on parchment-lined baking sheet and bake 10-12 minutes, flipping once halfway through.
06 - Combine mayonnaise, chopped pickles, capers, lemon juice, Dijon mustard, and parsley in a small bowl. Refrigerate until ready to serve.
07 - Lightly toast slider buns cut-side up under broiler or in a dry skillet until golden, about 1-2 minutes.
08 - Place crispy fish fillet on bottom bun half. Top with cheese slice (allow residual heat to melt slightly), lettuce, and generous dollop of tartar sauce. Crown with top bun and serve immediately.