Preparation

• In a 5- to 6-quart slow cooker, stir the chicken wings, all but 2 Tbs. of the scallions, the hoisin sauce, sesame oil, ginger, and sambal oelek until the wings are evenly coated. Cover and cook until the wings are cooked through, but not falling off the bone, 2-1/2 hours on high or 4 hours on low. (The wings can stay on the keep-warm setting for up to 1 hour.)
• Use tongs to transfer the chicken wings to a large foil-lined rimmed baking sheet. Strain the sauce into a fat separator and set aside for a few minutes. Pour the defatted sauce into a 2-quart saucepan, add the vinegar, and boil over high heat, stirring occasionally, until reduced by half, about 15 minutes.
• Position a rack 4 inches from the broiler element and heat the broiler on high. Brush the wings with the sauce and broil until browned, about 3 minutes. Turn the wings over, brush them again, and broil until browned and crisp, about 3 minutes more. Brush with the sauce once more before serving, topped with the remaining 2 Tbs. scallions and drizzled with the chile oil, if using. Serve any remaining sauce on the side for dipping.