To make the lemon mayonnaise, mix the mayonnaise, yogurt, lemon rind and juice, parsley and capers in a bowl. Cover and chill.

Cut the fish fillets into thin strips. Place the beaten egg in one shallow bowl. Mix together the breadcrumbs, sesame seeds, paprika and seasoning in another bowl. Dip  in the fish strips, one at a time, into the beaten egg, then into the breadcrumb mixture and toss until coated evenly. Lay on a clean plate.

Heat about 2.5cm/1in of oil in a frying pan until a cube of bread browns in 30 seconds. Deep-fry the strips in batches for 2-3 minutes, until lightly golden.

Remove with a slotted spoon, drain on kitchen paper and keep warm in the oven while frying the remainder. Garnish with watercress and serve hot with lemon wedges and the chilled lemon mayonnaise.