Open the cans of tuna and drain the liquid. Use a fork to flake the tuna into small pieces in a mixing bowl.

Finely chop the celery and red onion on a chopping board. This will add texture and flavor to the salad.

Measure out the mayonnaise, Dijon mustard, sweet pickle relish, and lemon juice.

In the mixing bowl with the flaked tuna, add the chopped celery, red onion, mayonnaise, Dijon mustard, sweet pickle relish, lemon juice, salt, and black pepper.

Using a fork, gently mix all the ingredients together until well combined. Be careful not to over-mix, as you want to maintain some texture.

Taste the tuna salad and adjust the seasoning with additional salt, pepper, or lemon juice as needed.

Spoon the tuna salad onto a plate or into a bowl. Garnish with chopped fresh parsley if desired.

Serve the tuna salad on a bed of lettuce, in a sandwich, or in a wrap.