Heat a large, heavy saucepan over medium heat. Add oil, onion and garlic. Cook, stirring frequently 2-3 minutes, or until onion is soft. Add cumin, salt and chile powder and cook 1 minute, until fragrant. Add broth and lentils. Bring mixture to a boil. Reduce heat, cover and simmer 10-15 minutes. Add sweet potatoes and kale and cook an additional 15-20 minutes until lentils and sweet potatoes are tender. Add water in small amounts, as necessary, during the cooking process. Stir in raisins. Serve over brown rice.