Waldorf Salad

Place apples, celery, and grapes in a medium bowl, and toss with juice of half the lemon. In another bowl, whisk together yogurt, mustard, honey, and juice of remaining half lemon. Pour half of the dressing over the apple mixture, tossing to combine. Serve over greens, drizzling remaining dressing over salad. Garnish the salad with chopped walnuts and snipped chives.