In a large pot, combine the beans with enough cold water to cover by 5 cm. Bring to a boil over high heat, and boil for 2 minutes. Remove from heat, cover the pot, and let stand for 1 hour. Drain well. (Beans can also be soaked overnight.)
In a large skillet, heat the oil over medium-high heat. Add the celery, onion, bell pepper, green onions and garlic. Cook, stirring often, until the onions are softened, about 6 minutes. Transfer to slow-cooker. Stir in the drained beans, water, beef broth, and red pepper. Bury the ham hock in the bean mixture. Cover and slow-cook until the beans are very tender, 9 to 10 hours on low. Remove the ham hock. Remove meat and discard rest. Return meat to pot, and stir in salt. Serve beans in bowls, spooned over hot cooked rice, and sprinkled with chopped green onions.