Drain the mandarins on a sieve. Clean, wash and thinly slice the celery. Cut the cheese into thin strips. Mix all ingredients together. Clean, wash and drain lamb's lettuce and radicchio.
Meanwhile, for the vinaigrette, mix mustard, vinegar and 3 tablespoons of water. Whip the oil into the vinaigrette, season with salt and pepper and pour over the cheese salad. Arrange lamb's lettuce and radicchio on a plate.
Place the cheese salad on top. Coarsely chop the walnuts and sprinkle them over the salad. Serve with 1/2 slice of wholemeal bread.