Prepare the ingredients.
Drain the tuna well and flake it into a medium mixing bowl with a fork. This helps break up large chunks and gives your salad an even texture.
Mix the dressing.
In a small bowl, stir together the mayonnaise, Dijon mustard, and lemon juice until smooth. This blend gives your tuna salad its creamy base with a bright, tangy finish.
Combine everything.
Add the celery, red onion, and pickle relish to the tuna. Pour the dressing over the top and gently mix with a fork until evenly coated. The mixture should look creamy but still hold its shape, not soupy.
Season and adjust.
Taste and add salt and pepper as needed. If you like more zip, add an extra squeeze of lemon or a touch more mustard.
Chill and serve.
Cover and refrigerate for at least 30 minutes to let the flavors meld. Serve cold on bread, in lettuce wraps, or with crackers.