Sauté the onions in the oil for about 10 minutes. Stir in the cayenne and garlic and sauté for a couple more minutes. Add the cabbage and sweet potatoes and sauté, covered for a few minutes. Mix in the juices, salt, ginger, cilantro, and tomatoes. Cover and simmer for about 15 minutes, until the sweet potatoes are tender. Add the okra and simmer for 5 minutes more. Stir in the peanut butter, place the pan on a heat diffuser, and simmer gently until ready to serve. Add more juice or water if the stew is too thick.