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 and wash the lettuce leaves, dab dry and pluck into bite-sized pieces. Rub the mushrooms with kitchen paper, clean them and cut them into fine leaves. Mix salad and mushrooms. Pour vinaigrette over the mushrooms and arrange on portion plates.
Serve sprinkled with diced tomatoes.