In a medium bowl, toss together apples and lemon juice. Add yogurt to coat completely. Set aside.
In a large bowl, stir chopped chicken, celery, raisins and walnuts. (See Note about walnuts)
Add the apples-yogurt to the bowl. Add mayonnaise and stir together.
Season with salt. Cover and chill until ready to serve. Serve within 3 hours.