Prepare the Vegetables: In a large bowl, add the chopped romaine lettuce, halved cherry tomatoes, diced cucumber, sliced red onion, and Kalamata olives.
Make the Dressing: In a small bowl, whisk together the olive oil, red wine vinegar, dried oregano, salt, and pepper.
Add Chicken and Feta: Top the salad with sliced grilled chicken and crumbled feta cheese.
Toss Together: Drizzle the dressing over the salad and gently toss to combine all ingredients.
Serve: Enjoy immediately or refrigerate for a short time before serving to let the flavors meld.