In a medium stock pot, heat oil over medium heat. Sauté onion and garlic in oil until soft. Stir in chili powder, oregano, tomatoes, broth, and water. Bring to a boil, and simmer for 5 to 10 minutes.
Stir in corn, , chiles, beans, cilantro, and chicken. Simmer for 10 minutes.
Ladle soup into individual serving bowls, and top with crushed tortilla chips, avocado slices, cheese, and chopped green onion