Drain the canned tuna thoroughly and place it in a large mixing bowl.

Finely chop the celery and red onion.

Add the mayonnaise and Dijon mustard to the tuna.

Mix well until the tuna is evenly coated.

Add the chopped celery and red onion to the tuna mixture.

Stir to combine.

Add the pickles or relish and lemon juice to the mixture.

Season with salt and black pepper to taste.

Mix all ingredients thoroughly until well combined.

Taste and adjust seasoning if necessary.

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