Spice filets with salt and pepper and fry them on both sides. Remove and allow to cool down. Peel and quarter apples and remove cores. Peel celery. Cut apples and celery into fine stripes. Boil celery stripes some minutes in salted water, drain and drip off. Cut chicken filets into small stripes and mix well with apples, celery, parsley and sour cream. Season to taste with salt, pepper and lemon juice. Marinade covered for about 30 minutes in refrigerator.
Remove skin, seeds and stalk from tomatoes and quarter them. Cut mushrooms into slices and fry them in a little bit oil, season with salt and pepper and drain them.
Arrange salad on plates and garnish with tomatoes and mushrooms.