Place the onion, garlic, carrots, sweet potatoes, garbanzo beans, and chicken breast pieces into a slow cooker. In a bowl, mix the cumin, turmeric, cinnamon, black pepper, parsley, and salt, and sprinkle over the chicken and vegetables. Pour in the tomatoes, and stir to combine.
Cover the cooker, set to High, and cook until the sweet potatoes are tender and the sauce has thickened, 4 to 5 hours.