In 4-quart saucepan, heat oil over medium-high heat. Cook onion in oil 2 minutes, stirring frequently, until tender.
Add remaining ingredients except chicken and green onions; heat to boiling, stirring occasionally. Reduce heat to low; cover and simmer 10 to 15 minutes to blend flavors.
Stir in chicken; cook 2 to 3 minutes or until chicken is hot. Top each serving with green onions.