Cut the fish fillets into four equal pieces and season on both sides with herb salt, paprika and ground curry.
Whisk the egg on a plate with fork. Spread the breadcrumbs in another plate. Dip the pieces of fish into beaten egg and coat in breadcrumbs.
Heat oil in a pan and fry the fish pieces from both sides until crispy and brown. Keep the fried fish pieces warm.
Cut the cornichons into thin slices.
Rinse, shake dry and pluck the lettuce leaves.
Toast the hamburger buns and split into halves.
Spread each bottom half of the buns with mayonnaise and top with half of the lettuce, one fried fish piece, cheese, remaining lettuce and cornichons. Sprinkle with ketchup and cover with the top halves.