For the mushroom salad, brush off the mushrooms and shorten the stems a little. Mix all ingredients together well and season strongly. Let stand for three to four minutes.
For the parsley mayonnaise, place all ingredients except the canola seed oil in a bowl and mix well. Gradually stir in the oil until evenly blended and creamy. Add water if necessary. Chill the mayonnaise in the refrigerator. Then serve with the mushroom salad.