Slice the Cucumbers and Onions – Slice the Persian cucumbers into thin rounds or half-moons. Thinly slice the red onion.
Make the Lemon Greek Vinaigrette – In a small bowl, whisk together lemon juice, extra virgin olive oil, dried oregano, salt, and black pepper.
Toss Everything Together – In a large bowl, combine cucumbers, red onions, feta, dill, and parsley. If using, add cherry tomatoes and kalamata olives. Drizzle with the vinaigrette and toss to coat.
Serve Right Away or Let It Sit – Serve immediately or let it sit for 10 minutes to enhance the flavors.