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 - Arrange 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 evenly on all sides.
05 - For frying: cook fish in batches 2-3 minutes per side until golden brown and fish flakes easily. For baking: place on parchment-lined baking sheet and bake 10-12 minutes, turning once halfway through.
06 - Combine mayonnaise, chopped pickles, capers, lemon juice, Dijon mustard, and fresh parsley in a medium bowl. Mix thoroughly and refrigerate until assembly.
07 - Lightly toast slider buns cut-side up in the oven for 2-3 minutes or in a dry skillet until golden.
08 - Place crispy fish fillet on bottom bun. Top with cheese slice, lettuce, and generous dollop of tartar sauce. Crown with top bun and serve immediately while hot.