Dissolve bouillon in 1 1/4 cups boiling water. Combine soy sauce, cornstarch, sugar, and ginger; stir into bouillon mixture.
Heat oil in a large skillet. Add chicken, and cook until browned, stirring often. Stir in bouillon mixture; cook over low heat, stirring constantly, 1 minute or until thickened. Add mushrooms and next 3 ingredients to skillet; saute 5 minutes or until tender.