In a small saucepan, combine the first 4 ingredients. Bring to a boil over medium-high heat. Remove from heat; set aside half the mixture for serving., Thread peppers onto 2 metal or soaked wooden skewers. Thread chicken onto 6 metal or soaked wooden skewers. Grill chicken, covered, over medium heat until meat is cooked through, 10-12 minutes, turning occasionally and basting frequently with soy sauce mixture during the last 3 minutes. Grill peppers, covered, until tender, 4-5 minutes, turning occasionally. Grill onions, covered, until lightly charred, 1-2 minutes, turning occasionally. Serve chicken and vegetables with reserved sauce for dipping.