Poach the chicken in salted water, drain and then cool thoroughly. Add lemon juice to the apple pieces and mix well. Wash the lettuce leaves and soak in chilled water. Soak the walnuts in hot water for a few minutes.
Reserve a few walnut kernels for garnishing and chop the rest. Hang the skimmed milk yogurt in a muslin cloth for about fifteen minutes to remove excess fluid. Mix chicken, apples, pineapple, chopped walnuts and celery.
Add the drained yogurt, salt, white pepper powder and mix well. Spread lettuce leaves on a serving dish and arrange the salad on them. Garnish with walnut kernels and serve.