Peel onions and cut them into fine rings. Wash and quarter the tomatoes. Clean, wash and drain the lettuce well. Clean, wash and thinly slice the mushrooms.
Wash the fillet and dab dry. Heat 1 tablespoon of oil in a frying pan. Fry the fillet for 4-5 minutes on each side. Season with salt and pepper. Take out and let cool down.
Briefly sauté the onions in hot frying fat. Remove the pan from the stove. Stir in vinegar and 2 tablespoons of water. Season with salt, pepper and sugar. Fold in 2-3 tablespoons of oil. Wash and chop parsley and stir in.
Cut the salad into strips. Mix with tomatoes, mushrooms and the lukewarm marinade. Cut the chicken filet thinly and arrange with the salad. Sprinkle with coarse pepper. Baguette tastes good with it.