Mix together diced celery, diced onion, lemon juice and yogurt in a bowl. Open tuna, drain and add to mixture.
Cut an avocado in half, remove the pit but leave the insides intack. If you'd like you may cut a few lines horizontally, then vertically (like a tick-tack-toe design) for a cube shaped release of the avocado when eaten but it's not necessary really.
Pile your tuna mixture into the avocado halves and serve with a spoon to scoop out all the mixture, and avocado at the same time when eating it.
A simple, healthy and satisfying lunch!
