Rinse the beans, and soak overnight in 4 quarts of water. Drain and set aside. In a large pot, heat the olive oil. Add the onion, green pepper, and garlic and saute over low heat for 10 minutes. Add beans and ham hock, and enough water to cover. Stir in tomato paste and seasoning (except for vinegar). Bring to a boil, cover, and simmer for 2 hours. Let cool slightly.
Using a blender, remove half of the cooked beans and puree smooth. Return to pot. Add vinegar or sherry and stir well. Serve soup over white rice and top with fresh minced onion and fresh cilantro.