Slice the chicken breast into thin strips.
Combine the chicken with the olive oil, lemon juice, oregano, paprika, garlic powder, cumin, salt, pepper and the Greek yogurt if using. Set aside for at least 10 minutes.
Grate the cucumber and squeeze out as much liquid as possible.
Stir the cucumber together with the Greek yogurt, garlic, lemon juice, olive oil, salt and dill. Refrigerate until serving.
Heat a skillet over medium-high to high heat. Add the chicken in a single layer and cook 6 to 8 minutes, turning, until browned and cooked through.
Warm the pitas in a dry skillet 30 to 60 seconds per side, or in the air fryer at 350°F for 1 to 2 minutes.
Fill each pita with chicken, tzatziki, fries, lettuce, tomato, cucumber, red onion and feta if using.