Put the couscous in boiling salted water and let it stand for about 3 minutes. Wash the apple, quarter it and cut out the core. Cut apple quarter into pieces. Clean, wash and cut chicory into pieces.
Clean, wash and drain the lamb's lettuce. Wash marjoram, pluck off leaves and chop coarsely. Mix vinegar, 2 tablespoons water, salt, pepper and sugar. Fold in the oil. Stir in marjoram.
Mix all ingredients with the vinaigrette. Arrange in a bowl. Garnish with marjoram.