Drain the tuna well and use a fork to flake it into a medium mixing bowl, breaking it into flaky, bite-sized pieces.
Finely slice the celery into thin, crunchy slices and add them to the bowl, ensuring they’re evenly distributed for a crisp contrast.
Dice the red onion finely, then soak it in cold water for about 10 minutes to mellow its sharpness. Drain well and add to the mixture.
Scoop in the mayonnaise and gently fold it into the tuna mixture, coating the flakes evenly without breaking them apart too much.
Squeeze in the fresh lemon juice to brighten the flavors, then gently stir again until everything is well combined and has a creamy, vibrant appearance.
Stir in chopped parsley or dill for a fresh herbal note, followed by capers if using, for a briny punch.
Season with salt and freshly ground black pepper to taste, mixing gently and tasting to ensure balanced flavor.
Cover the bowl and chill in the refrigerator for at least 30 minutes to let the flavors meld and the texture set.
Give the salad a gentle stir, taste again, and adjust seasoning if necessary. It should look creamy with visible bits of celery and herbs.
Serve the tuna salad chilled on a bed of greens, with crusty bread, or as a filling for sandwiches. Garnish with extra herbs or lemon wedges for a fresh finish.