In a pan, heat oil. Gradually stir in flour. Let this form a paste. Then, gradually stir in the milk and continue stirring until thickened.
Add chicken to white sauce mixture. Add sugar, salt, pepper, and garlic powder. Mix well and simmer for 20 minutes over low heat.
If soup is not as thick as desired, mix a small amount of corn starch with a small amount of water and add to soup. Simmer for 5 minutes.