In a medium bowl, whisk 2 tablespoons of olive oil, lemon juice, minced garlic, oregano, salt, and pepper.
Add the diced chicken to the marinade and let rest for 15 minutes.
Bring a large pot of salted water to a boil and cook penne pasta according to package instructions until al dente.
Drain the pasta, reserving 0.25 cup of the pasta cooking water.
Heat the remaining 1 tablespoon of olive oil in a large skillet over medium-high heat.
Add the marinated chicken to the skillet and cook until browned and internal temperature reaches 165F, approximately 6 to 8 minutes.
Add the cherry tomatoes and red onion to the skillet, sautéing for 2 minutes until the vegetables soften slightly.
Toss the cooked pasta and reserved pasta water into the skillet with the chicken mixture.
Remove from heat and fold in the kalamata olives and crumbled feta cheese.
Top with diced cucumber and fresh parsley before serving.