In a mixing bowl, combine the drained tuna, mayonnaise, Dijon mustard, and lemon juice. Use a fork to break up the tuna and mix the ingredients until well blended.
Add the chopped celery, red onion, and sweet pickle relish to the bowl. Stir everything together until evenly mixed.
Taste the mixture and season with salt and black pepper according to your preference. Mix again to incorporate the seasoning.
For serving, you can either serve the tuna salad directly in a bowl, or on a bed of lettuce leaves with slices of tomato if desired.
Enjoy your tuna salad either as is or spread on your favorite bread for a delicious sandwich.
For added crunch, feel free to incorporate diced bell peppers or chopped pickles.
This salad can be stored in an airtight container in the refrigerator for up to 3 days.
Serve with crackers or pita chips for a delightful snack option.