Fine sea salt and freshly cracked pepper, to taste
Thoroughly drain the tuna and place in a large bowl. Add the finely chopped celery, finely chopped red onion (drained if you soaked in water), pickle relish, parsley, mayo, dijon mustard, lemon juice, olive oil, and salt + pepper to taste.
Stir to combine and enjoy immediately OR separate into meal prepping containers.
To meal prep: separate the tuna salad into 3 or 4 parts and place in airtight containers. In separate containers/bags add some sides such as fresh vegetables, fresh fruits, pita chips, whole grain bread, etc.