Wash parsley, dab dry and chop finely. Mix vinegar, salt, pepper, sugar and parsley. Whip the oil into the mixture. Clean, wash, quarter, seed and finely chop the tomatoes.
Clean the salad, wash, dab dry and pluck into bite-sized pieces. Wash and clean the mushrooms and cut them into thin slices. Mix salad and mushrooms. Pour vinaigrette over them and arrange on four plates.
Serve garnished with diced tomatoes.