Add potatoes to a large pot of salted water. Bring to a boil and cook until fork-tender (about 10–15 minutes). Drain well.
While the potatoes are cooking make the dressing. In a large bowl, whisk together olive oil, lemon juice, lemon zest, garlic, oregano, salt, and pepper.
Add the warm, drained potatoes straight into the bowl with the dressing and toss gently. This helps them soak up all that flavor.
Let cool slightly, then mix in feta, red onion, parsley, and any extras like cucumber or tomatoes.
You can serve it slightly warm or refrigerate for 1–2 hours for even more flavor.