Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius).
On a large sheet pan, combine the chicken strips, sliced bell peppers, and red onion.
Drizzle with olive oil and sprinkle with dried oregano, garlic powder, salt, and black pepper. Toss to coat evenly.
Spread the mixture in a single layer and roast for 20 minutes, or until chicken reaches an internal temperature of 165 degrees Fahrenheit.
In a small bowl, whisk together Greek yogurt, dill, parsley, lemon juice, and minced garlic to create the herby ranch.
Warm the pitas slightly, then stuff with the roasted chicken and vegetable mixture and drizzle with the herby ranch dressing.