Clean the spring onions, cut the white and light greens diagonally into rings and fry in 1 teaspoon oil until translucent. Deglaze with broth and season with lemon juice, salt, pepper and sugar. Peel the potatoes, cut into slices and mix with the sauce. Quarter and core the apple, cut the quarters crosswise into slices. Peel, quarter and finely chop the piece of cucumber. Fold both under the salad.
Season the fish with salt and pepper, turn in flour and knock off a little. Fry in 1 teaspoon oil with the butter on each side for 3 minutes until golden brown.
Season the potato salad to taste and serve with the fish.