Preheat oven to 425˚F.
Pour melted butter over Panko crumbs and work into the crumbs to evenly distribute. Season the crumbs with Old Bay, onion and garlic powders, lemon zest, thyme and chives.
Season the fish with salt and pepper, and coat in egg whites, then crumbs and arrange on slotted broiler pan or cooling rack arranged over baking sheet. Bake 20 minutes or until deeply golden and crispy, and dress with lemon juice or malt vinegar.
Serve on toasted muffin or muffin bread with slaw or shredded lettuce. Top with pickles and onions, and muffin top or toasted muffin bread.