In a 3- or 4-qt. slow cooker, combine the first 14 ingredients. In a small skillet, heat oil over medium heat. Add onion; cook and stir until tender, 5-7 minutes. Add garlic and ginger; cook 1 minute longer. Stir into slow cooker.
Cook, covered, on low until chicken is cooked through and vegetables are tender, 5-6 hours. Serve with couscous; sprinkle with cilantro.
