01 - Preheat oven to 400°F. Lightly grease a 9x13-inch baking dish with oil or nonstick spray.
02 - Coat chicken thighs evenly with olive oil, then season generously 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-high heat, then reduce to a simmer and cook for 10 minutes until the peaches are soft and broken down. Blend with an immersion blender or transfer to a standard blender and puree until smooth.
04 - Pour half of the peach BBQ sauce over the chicken thighs, spreading to coat evenly. 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 caramelized. For extra browning, broil for 2 to 3 minutes at the end.
06 - Remove from the oven and let the chicken rest for 5 minutes. Garnish with chopped cilantro or parsley if desired, and serve with the remaining peach BBQ sauce on the side.