In a large skillet, heat oil over medium-high heat. Add onion and cook, stirring occasionally, for 3 minutes or until golden. Add sweet potatoes and cook, stirring occasionally, for 10 minutes.
Add 2 cups water, raisins, light-brown sugar, salt, ginger, cinnamon and cayenne pepper. Cook, covered, over medium heat 12 minutes or until tender. Stir occasionally.