In a large mixing bowl, whisk together olive oil, oregano, garlic powder, salt, and pepper until well combined. Add the chicken thighs to the marinade and coat well. Cover and marinate in the refrigerator for at least 30 minutes.

Heat a large skillet over medium-high heat. Add the marinated chicken thighs and cook for 5-7 minutes on each side until golden brown and cooked through.

In a medium bowl, mix together Greek yogurt, feta cheese, lemon juice, minced garlic, salt, and pepper until smooth and well combined. Adjust seasoning as desired.

Slice the cooked chicken into strips. On warm pita, spread tzatziki, add chicken, and top with cherry tomatoes, cucumber, and red onion. Roll up tightly to serve.