In a small saucepan, combine the broth, ginger and garlic; bring to a boil. Reduce heat; simmer, uncovered, for 15 minutes. Remove and discard ginger and garlic.
Combine cornstarch and water until smooth; gradually stir into broth. Bring to a boil; cook and stir for 2 minutes or until thickened. Add chicken; heat through. Reduce heat. Drizzle beaten egg into hot broth, stirring constantly. Remove from the heat; stir in onion.