Preheat the oven to 425°F. Line a large sheet pan with parchment paper.
In a large bowl, combine the chicken pieces, olive oil, garlic powder, onion powder, smoked paprika, salt, black pepper, and cayenne pepper (if using). Toss until the chicken is well coated.
Spread the seasoned chicken evenly on the prepared sheet pan. Add the cherry tomatoes and cucumber around the chicken.
Bake in the preheated oven for 20-25 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F.
While the chicken is baking, prepare the herby ranch slaw. In a large bowl, combine the shredded cabbage, red onion, parsley, dill, and ranch dressing. Toss until well mixed.
Once the chicken is done, remove the sheet pan from the oven and let it cool for a few minutes.
To assemble the pitas, cut each pita in half and fill with the chicken mixture and herby ranch slaw. Serve immediately.