Preheat the oven to 375°F (190°C).

In a bowl, mix together hoisin sauce, soy sauce, honey, oyster sauce, rice vinegar, minced garlic, Chinese five-spice powder, and sesame oil.

Place the chicken thighs in a large resealable plastic bag.

Pour half of the marinade over the chicken. Seal the bag and refrigerate for at least 2 hours, or up to overnight. Cover and refrigerate the remaining marinade separately.

Remove the marinated chicken from the refrigerator and let it sit at room temperature for about 30 minutes.

Place the chicken thighs on a baking sheet lined with aluminum foil.

Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through.

While the chicken is cooking, transfer the reserved marinade to a small saucepan. Bring it to a boil, then reduce heat and simmer for about 10 minutes to thicken.

Brush the cooked chicken with the thickened marinade.

Broil the chicken for an additional 2-3 minutes, watching closely to avoid burning.

Once the chicken is caramelized and slightly charred, remove it from the oven.

Let the char siu chicken rest for a few minutes before slicing and serving.