Cut potatoes into slices and cook in boiling salted water for about 15 minutes
Wash the meat briefly under cold water and dab dry. Heat 1 teaspoon of oil in a small coated pan. Fry the chicken filet in it for about 10 minutes, turning it over. Season with salt and pepper. Remove and keep warm
Cut onion into fine rings and heat in 1 teaspoon of oil in the frying fat. Add onion and mushrooms and fry well. Season with salt and pepper. Take out everything
Deglaze the hot frying fat with vinegar and 2 tablespoons of water. Stir in mustard. Season marinade with salt, pepper and sweetener. Cut tomatoes into slices. Mix with potatoes, mushrooms, onions and the marinade. Season again if necessary and arrange on a plate. Cut the fillet open and arrange on the salad. Sprinkle with chives