Method
In a medium mixing bowl, combine the drained tuna and mayonnaise. Use a fork to break up the tuna into small, even pieces and mix until fully coated.
Add the celery, red onion, lemon juice, Dijon mustard, salt, and black pepper to the bowl. Stir gently but thoroughly to combine all ingredients.
Taste the tuna salad and adjust seasoning if needed, adding more salt, pepper, or lemon juice to your preference.
For best flavor, cover the bowl with plastic wrap and refrigerate for at least 15 minutes to allow the flavors to meld.
Serve the tuna salad chilled, either on its own, as a sandwich filling, or with crackers or lettuce wraps.
Notes
For best flavor, refrigerate for at least 15 minutes before serving.