Heat oil in a nonreactive soup pot over medium heat. Add onions and sauté until
translucent, stirring occasionally, about five minutes.
Add flour to form a roux. Allow roux to cook for two minutes.
Add broth and spices, whisk well. Turn heat to high; continue to whisk until
mixture comes to a boil and thickens. Reduce heat to low and add green chiles. Allow
mixture to come back to a gentle boil, stirring occasionally, about an hour.
Add tomatoes and chicken. Stir well and bring mixture back to a boil, stirring