In a medium bowl, flake the drained tuna with a fork.

Add the chopped Kalamata olives, sun-dried tomatoes, diced red onion, and chopped fresh parsley to the bowl with the tuna.

In a small separate bowl, whisk together the lemon juice, extra virgin olive oil, and Dijon mustard.

Pour the dressing over the tuna mixture. Season with salt and black pepper.

Gently toss all ingredients until well combined. Taste and adjust seasoning as needed.

Spoon the tuna salad mixture into crisp romaine lettuce leaves or hollowed-out bell pepper halves.