In a medium bowl, combine hoisin sauce, soy sauce, honey, rice vinegar, sesame oil, five-spice powder, garlic powder, and ginger powder to create the marinade. Whisk until well combined.
Place the chicken thighs in a resealable plastic bag or a shallow dish and pour the marinade over the chicken. Ensure all pieces are well coated. Seal the bag or cover the dish and refrigerate for at least 1 hour (or up to overnight for deeper flavor).
Preheat your oven to 425°F (220°C).
Line a baking sheet with aluminum foil and place a wire rack on top of it. Arrange the marinated chicken thighs on the wire rack, allowing excess marinade to drip off.
Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and has a nice caramelized exterior. You may want to baste the chicken with the remaining marinade halfway through for extra flavor.
For an additional char, broil the chicken for the last 2-3 minutes, keeping a close eye to prevent burning.
Remove the chicken from the oven and let it rest for a few minutes before slicing it into strips.
Serve the Char Siu Chicken garnished with sliced green onions and a sprinkle of sesame seeds.