Heat the oil in a large saucepan over medium heat. Add the onion and cook until soft and translucent, about 3 minutes. Add the garlic, chiles, cumin, oregano, and cayenne pepper and continue to sauté for 1 more minute.
Add the beans, chicken broth, and chicken and cook over low heat for 1 hour. Season with salt and pepper, to taste.
Serve the chili in individual bowls topped with shredded cheese, if desired. Garnish with cilantro, salsa, chopped scallions, and/or guacamole.