In large saucepan, heat oil over medium heat; cook onion and garlic for 2 or 3 minutes or until softened. Add carrots, celery, salt, pepper and oregano; cook for 6 to 8 minutes or until carrots and celery are softened.
Add chicken broth and bring to boil. Reduce to simmer; cook noodles and chicken for 8 to 10 minutes or until noodles are tender.