Combine soy sauce, brown sugar, peanut butter, hoisin sauce, ginger, garlic, and chile paste in a resealable container. Mix well. Stir in cornstarch. Add chicken to marinade, cover, and refrigerate for at least 30 minutes.
Preheat the oven to 400 degrees F (200 degrees C). Line a jelly roll pan or rimmed cookie sheet with a double layer of foil large enough to envelop the chicken.
Spread chicken evenly over the bottom layer of foil. Top with the marinade, fold the upper layer of foil on top, and wrap to fully cover chicken.
Roast in the preheated oven until chicken thighs are no longer pink, about 1 hour. Unwrap and sprinkle with cilantro.