Dice the celery, chop up the hard-boiled egg, and get the rest of the ingredients nearby.
Open the can of tuna and squeeze out the excess water.
Add the tuna in a medium-sized mixing bowl and break it up. Not too much, though. The chunks look nice when serving; however, the more you break it up, the further it will go.
Add the celery, egg, dill, relish, mustard, and a little mayonnaise. Mix it with a fork, being careful not to overwork it. Adjust the amount of mayonnaise depending on how you like it or if you are on a diet or not.