Crispy Fish Sandwich

Name: Crispy Fish Sandwich
Ingredients: 1 small red onion, thinly sliced into rounds; 4 oz. bread-and-butter pickles, plus ½ cup brine; ¾ cup mayonnaise; ⅓ cup chopped dill; 2 tsp. hot sauce; 1 tsp. freshly ground black pepper; 2 tsp. fresh lemon juice, plus wedges for serving; 1 Tbsp. kosher salt, divided; 2 large eggs, lightly beaten; 1½ cups panko (Japanese breadcrumbs); ½ cup all-purpose flour; 2 flounder fillets (about ⅔ lb. total), cut in half crosswise on a diagonal; ⅔ cup vegetable oil; 3 cups shredded iceberg lettuce; 8 slices Pullman bread; 1 cup potato chips, plus more for serving