Place the avocado in a bowl and put lemon juice and sea salt on top. Mash with fork.
Toss tuna, mayo or yogurt, mustard, red pepper flake, celery, red onion and parsley in the bowl with mashed avocado. Combine and season with salt and pepper to taste. I like it on toasted wheat bread with pickles, romaine lettuce and sliced tomato.
Recipe by pretty plain janes at https://prettyplainjanes.com/2016/03/03/avocado-tuna-salad/