Drain the water from the tuna and transfer the tuna to a bowl. Use a fork to break up the tuna.
To the tuna, add the mayonnaise, relish, diced celery, celery salt and pepper. Stir to combine. Taste and adjust seasonings, if desired.
Core the tomatoes with a small sharp knife. Use a small spoon to scoop out the flesh and seeds, leaving a small layer of flesh next to the skin.
Sprinkle the kosher salt inside of the tomatoes.
Use a small spoon to scoop the tuna salad into the hollowed-out tomatoes. Press down gently as you fill the tomatoes.
If desired, garnish with minced parsley. Serve.
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Notes
Please note that I am not a medical or nutritional professional. I provide nutritional information for my recipes as a courtesy to my readers. It is calculated using the LoseIt! calculator. While I attempt to provide information that is as accurate as possible, you should calculate the nutritional information independently before relying on it.