In a large bowl, combine olive oil, oregano, garlic powder, and salt and pepper to taste. Add chicken thighs, ensuring each piece is well-coated. Cover and let marinate in the refrigerator for at least 30 minutes.

Heat a skillet over medium-high heat. Once hot, add the marinated chicken thighs and cook for 5-7 minutes per side until golden brown. Ensure the internal temperature reaches 165°F (75°C). Remove from skillet and let rest before slicing.

In a mixing bowl, combine Greek yogurt, crumbled feta, lemon juice, and minced garlic. Stir until smooth and creamy, seasoning with salt and pepper. Set aside.

Spread a generous amount of tzatziki sauce on warm pita bread. Add sliced cooked chicken, cherry tomatoes, cucumber, and red onion.

Roll the pita tightly around the filling. Serve immediately with extra tzatziki on the side.