Combine first 5 ingredients in a medium bowl; stir well.
Peel eggs, discarding 3 yolks. Chop egg whites and remaining 3 yolks; stir into yogurt mixture. Add ham and celery; stir gently. Sprinkle with pepper. Cover and chill 15 minutes or until ready to serve.
Remove soft bread from center of French bread loaf. Reserve soft bread for another use. Fill center of loaf with salad. Cut into four equal sandwiches, and serve immediately.