Cook the pasta according to package instructions. Drain and rinse under cold water to cool.

In a large mixing bowl, combine the cooked pasta, tuna, cherry tomatoes, cucumber, and red onion.

In a small bowl, whisk together the olive oil, lemon juice, dijon mustard, salt, and black pepper.

Pour the dressing over the pasta mixture and toss gently to combine. Garnish with fresh parsley.

Chill in the refrigerator for at least 30 minutes before serving for best flavor.