Peel the potatoes and cut into 1.5 cm cubes. Peel the cucumber, halve lengthways, remove the seeds and cut into approx. 1 cm wide pieces, cut the pepper into 1 cm cubes. Peel and grate the horseradish.
Heat the oil in a pan. Fry the potatoes for approx. 5 minutes, add the pepper and cucumber and continue to fry for approx. 5 minutes until the potatoes are golden brown. Deglaze with wine, reduce and then flavour with soy sauce, salt and pepper.Cut the fish into portions, remove any bones and season with salt and pepper. Heat the butter in a pan and fry on both sides.
Serve with the vegetables and garnish with the horseradish.