In a large saucepan, heat oil over medium-high heat. Add onion and garlic, and cook until onion is soft, about 4 minutes. Mix in green chilis, corn, flour, and cumin. Stir in broth and enchilada sauce. Bring to a simmer.
Add shredded chicken, and let soup simmer 15 minutes, until slightly thickened.
Top soup with avocado and, if desired, cheese, tortilla chips, and cherry tomatoes.
