In a medium stock pot, heat oil over medium heat. Saute 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, hominy, 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.