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. Drizzle with olive oil and season generously with kosher salt and black pepper on all sides. Arrange in the prepared baking dish, skin-side up.
03 - In a medium 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-high heat, then reduce to a simmer. Cook for 10 minutes until the peaches break down and soften. Puree with an immersion blender or transfer to a standard blender and blend until smooth.
04 - Pour half of the peach BBQ sauce evenly over the seasoned chicken thighs, using a spoon or brush to coat each piece thoroughly. Arrange fresh peach slices around and on top of the chicken. Reserve the remaining sauce for serving.
05 - Bake uncovered for 35 to 40 minutes, or until the chicken reaches an internal temperature of 165°F and the skin is deeply caramelized. For additional browning, broil on high for 2 to 3 minutes at the end of baking, watching carefully to prevent burning.
06 - Remove from the oven and let the chicken rest for 5 minutes to allow juices to redistribute. Garnish with chopped fresh cilantro or parsley if desired. Serve warm with the reserved peach BBQ sauce drizzled on top or alongside.