In a large saucepan, heat the oil.  Add the onion, bell pepper, celery, and garlic, and cook for 7 minutes over medium heat, stirring frequently.  Stir in the tomatoes and cook for 3 to 4 minutes more.  Stir in the beans and seasonings and cook for about 30 minute over medium-low heat, stirring occasionally.

In a medium saucepan, place the sweet potatoes in enough boiling water to cover.  Cook for about 15 minutes over medium heat, until tender, and drain in a colander.  

When the chili has cooked for about 25 minutes, stir the potatoes into the pot.  

Ladle the chili into bowls and garnish with chopped red onion or scallions.

Makes 6 servings.