In a 5- to 6-qt. slow cooker combine the first 11 ingredients (through cayenne pepper). Cover and cook on low 6 to 8 hours or high 3 to 4 hours. Using a handheld immersion blender, blend soup until smooth. (Or let soup cool slightly. Transfer soup in batches to a food processor or blender. Cover and process or blend until smooth.) Stir in coconut milk. If desired, top servings with cilantro.