Cut each avocado in half, and remove the pit from the center.
Use a spoon to scoop out a bit of the center of each avocado so that you have room to fill it with the tuna salad.
In a small mixing bowl, add the drained tuna.
Mix in the mayo, dijon mustard, celery, onion, garlic as well as salt and pepper to taste. Stir to combine well.
Add the finished tuna salad to the center of each avocado half, and serve garnished with some freshly chopped parsley. A serving is one whol avocado filled with half of the tuna salad mixture.
Enjoy!