Instructions:
- Drain the tuna thoroughly. If using tuna in oil, gently press out the excess oil. Transfer the tuna to the large mixing bowl and flake it gently with a fork until mostly broken down but still possessing some texture.
- Finely dice the celery and mince the red onion. Roughly chop the capers, parsley, and dill.
- Add the diced celery, minced onion, capers, parsley, and dill directly into the bowl with the flaked tuna.
- In a small separate bowl, whisk together the mayonnaise, Dijon mustard, lemon juice, and apple cider vinegar until smooth.
- Pour the dressing mixture over the tuna and vegetables. Gently fold everything together using a spatula until just combined. Do not overmix.
- Season generously with freshly ground black pepper and salt. Taste and adjust seasoning as needed.
- Cover the bowl tightly and refrigerate for a minimum of 30 minutes to allow the flavours to meld before serving.