Mix olive oil, dried oregano, garlic powder, salt, and pepper in a bowl. Add chicken thighs and coat thoroughly. Marinate for at least 30 minutes, or overnight in the refrigerator for deeper flavor.

Heat a skillet over medium-high heat until hot. Cook the marinated chicken thighs for 5-7 minutes per side without moving them too much, until golden brown and cooked through to an internal temperature of 165°F (74°C).

While chicken cooks, prepare tzatziki sauce by mixing Greek yogurt, crumbled feta cheese, lemon juice, minced garlic, salt, and pepper in a bowl until smooth. Taste and adjust seasoning as needed. Add a small amount of fresh dill if desired.

Transfer cooked chicken to a cutting board and let rest for 3-5 minutes, then slice into strips.

Warm pita breads in a dry skillet for about 30 seconds per side, or wrap in foil and heat in a 350°F oven for 5 minutes until soft and pliable.

To assemble, spread 2-3 tablespoons of feta tzatziki down the center of each warm pita. Layer sliced chicken strips on top.

Add halved cherry tomatoes, diced cucumber, and thinly sliced red onion, distributing vegetables evenly across the chicken.

Fold the bottom of the pita up about an inch, then roll tightly from one side to the other, keeping everything wrapped inside.

Garnish with fresh parsley if desired and serve immediately with extra tzatziki on the side for dipping.