Rinse beans and place in a large bowl. Cover beans with 4 inches of water and soak overnight (or 8 hours). Strain and rinse black beans.
In a large soup pot, heat the oil over medium heat. Add onion and jalapeno and saut for 10 minutes, until soft.
Add beans and vegetable broth or water. Stir in ginger, allspice, thyme and salt. Bring to a boil, then reduce heat and simmer for 1 hour 30 minutes.
Add sweet potatoes and brown sugar and simmer for an additional 30 minutes, until beans and sweet potatoes are soft.
Puree 1 cup of the soup in a blender and then add it back into the soup pot. Stir in cilantro and green onion. Salt and pepper to taste.