1. Preheat the grill pan over medium-high heat.
2. Season the chicken breasts with salt, pepper, and half of the oregano.
3. Grill the chicken for about 6-7 minutes on each side, or until fully cooked. Let it rest for a few minutes, then slice.
4. In a large mixing bowl, combine cherry tomatoes, cucumber, red onion, kalamata olives, and feta cheese.
5. In a small bowl, whisk together olive oil, red wine vinegar, remaining oregano, salt, and pepper.
6. Add the grilled chicken slices to the salad and drizzle with the dressing. Toss to combine.
7. Serve immediately and enjoy!