Heat the broth to a simmer in a soup pot and poach the chicken breasts until done, about 10 - 15 minutes. Remove the chicken to a plate and shred with two forks. Pour the broth off into a bowl (or use another pan to make the soup in).
Heat the oil and cook the onion and garlic until soft, about 5 minutes. Stir in the chili powder, cumin, and oregano and cook a minute, then add the tomatoes and broth. Bring to a simmer and cook 10-20 minutes.
Stir in the corn, chilies, beans, cilantro, and chicken and simmer another 20 minutes or so.
Serve the soup and have tortilla chips, cheese, green onions, and avocado slices in bowls to pass around.