Make the dressing. In a small bowl or jar, whisk together lemon zest, lemon juice, olive oil, garlic, Dijon, oregano, salt, and pepper until emulsified.
Prep the vegetables. Dice the cucumber, halve the tomatoes, finely chop the red onion, and slice the olives.
Roughly chop parsley and mint.
Combine the base. In a large bowl, add the chickpeas, tuna (flaked with a fork), cucumber, tomatoes, red onion, olives, and capers.
Toss with dressing. Pour the dressing over the salad and gently toss until everything is well coated. Taste and adjust salt, pepper, or lemon.
Add herbs and feta. Fold in parsley, mint, and feta (if using). Give it one more gentle toss.
Rest, then serve. Let the salad sit for 10–15 minutes if you can.
This helps the flavors meld. Serve at cool room temperature or chilled.