Scoop out some of the avocado flesh with a spoon to make the holes larger to stuff the salad, leaving a small border. Dice the avocado that was scooped out and add it to a small bowl.
Add the albacore tuna, celery, red onion, drill, mayo, mustard, lemon juice, salt, and pepper to the bowl. Combine. Adjust the seasonings to taste if you want more mayo, more herbs, etc.
Spoon the tuna mixture into the 4 avocado halves. Garnish with more fresh herbs. Enjoy! Best eaten right away.
Notes
This can make 2-4 servings depending on how many calories or how much protein you're trying to eat. Avocados to have a fair amount of healthy fats, you can reduce the overall fat in the recipe by swapping some of the mayo for light Greek yogurt.