01 - Preheat oven to 400°F. Lightly grease a 9x13-inch baking dish with cooking spray or oil.
02 - Pat chicken thighs dry with paper towels. Rub with olive oil, then season evenly with kosher salt and black pepper. Arrange in the prepared baking dish, skin-side up.
03 - In a small saucepan, combine the 2 sliced peaches, ketchup, apple cider vinegar, honey, brown sugar, Dijon mustard, Worcestershire sauce, smoked paprika, garlic powder, and onion powder. Bring to a boil over medium heat, then reduce to a simmer and cook for 10 minutes until the peaches are soft and broken down. Purée with an immersion blender or transfer to a standard blender and blend until smooth.
04 - Pour half of the peach BBQ sauce over the seasoned chicken thighs, spreading it evenly to coat each piece.
05 - Tuck fresh peach slices around and on top of the chicken thighs. Reserve the remaining BBQ sauce for serving.
06 - Bake uncovered for 35-40 minutes, until the chicken reaches an internal temperature of 165°F and the skin is caramelized. For additional browning, broil for 2-3 minutes at the end of baking.
07 - Remove from the oven and let the chicken rest for 5 minutes. Garnish with chopped fresh cilantro or parsley if desired. Serve with the reserved peach BBQ sauce on the side.