In a medium bowl, combine chicken thighs, olive oil, dried oregano, garlic powder, paprika, salt, and black pepper. Toss until the chicken is well coated. Let it marinate for at least 15 minutes (or up to 2 hours in the fridge for deeper flavor).
Heat a large skillet or grill pan over medium-high heat. Add the marinated chicken thighs. Cook for about 6-7 minutes on each side or until the chicken is cooked through and has a nice sear. Remove from heat and let it rest for a few minutes.
Once slightly cooled, slice the chicken thighs into thin strips.
In the same skillet or grill pan, lightly warm the pita breads until they are soft and pliable, about 1 minute per side.
Spread a generous amount of tzatziki on each warm pita. Add sliced chicken, followed by cherry tomatoes, diced cucumber, and red onion.
Top with fresh parsley leaves for an extra burst of flavor and color.
Roll up the pita around the fillings and serve them with extra tzatziki on the side if desired.