Gather all your ingredients on hand.

Wash the cherry tomatoes and cut them in half. Dice the cucumber and finely chop the red onion.

In a large mixing bowl, add the drained tuna and break it into smaller pieces. In a separate bowl, whisk together olive oil, red wine vinegar, dried oregano, salt, and pepper.

Pour the dressing over the tuna and add the prepared vegetables, olives, feta cheese, and parsley. Gently toss until evenly coated.

Cover and chill in the refrigerator for at least 30 minutes before serving.