1. Bring chicken broth to a simmer in a two-quart saucepan. Add soy sauce, shredded chicken, mushrooms, and crushed garlic. Simmer for five minutes.
2. Add chili powder, white pepper, vinegar, bamboo shoots, and tofu. Simmer for five minutes.
3. Combine cornstarch with cold water in a cup. Stir until mixture is smooth. Add to soup and stir well. Simmer for five minutes until soup is thickened.
4. Beat egg in a cup until yolk and white are combined. Pour beaten egg slowly, in a fine stream, into soup. Stir soup several times. Wait 30 seconds. Add scallions and sesame oil to soup. Stir well.
5. Remove from heat and serve hot.