Separate the whites and the yolks of the eggs. Set aside 2 yolks for another use.
Chop the egg whites.
In a large bowl, combine the avocado, egg yolks, and yogurt. Mash until the mixture is creamy and smooth. Then mix in the lemon juice and zest, salt and pepper.
Stir in the egg whites, celery, and optional onion. Cover and refrigerate, or serve immediately as a sandwich, a wrap, or on a bed of lettuce. I enjoy this as a chunky dip with celery and carrot sticks. It is equally delicious served alongside sliced tomatoes.