In a large bowl, flake the tuna with a fork. It should resemble chunky tuna confetti—purposefully imperfect.
Add tomatoes, cucumber, red onion, olives, feta, capers, and parsley. Give it a quick toss so everything starts mingling.
Mix in olive oil and lemon juice. If you’re using zest, grate a little over the top for a bright, sunny finish.
Season with salt, pepper, and oregano if you’re feeling fancy. Taste and adjust—you’re the boss here.
Let it sit for a few minutes if you can. This helps the flavors get cozy and acquainted.