Drain mandarin oranges on a sieve. Collect the juice. Mix mustard, yoghurt and mayonnaise. Season to taste with 2 tablespoons of fruit juice. Season with salt. Coarsely chop the walnuts, except for some for garnishing, and fold them into the mustard cream.
Cut the cheese into fine sticks. Carefully fold cheese and mandarin oranges into the mustard cream. Clean the salad, wash and pat dry. Cut lettuce into narrow strips, except for a few leaves. Wash chives, dab dry and cut into small rolls.
Fold the salad into the mustard cream shortly before serving. Garnish the cheese cocktail with salad leaves and walnut halves and sprinkle with chive rolls.