In a 3 ½- to 4-quart slow cooker place onion and mango. Top with chicken, chipotle pepper, garlic, salt, cumin, ginger, and cinnamon. Pour tomatoes, chicken broth, and mango nectar over all. Cover and cook on low-heat setting for 4 to 5 hours or on high-heat setting for 2 to 2½ hours. Using a slotted spoon, remove chicken from cooker; cool slightly.