Heat oil in 10" skillet over medium-high heat. Add onions and cook until they begin to brown, stirring occasionally. Reduce heat to medium. Cook until onions are tender and caramelized, stirring occasionally. Remove skillet from heat.
Heat broth, black pepper, carrots and celery in 4-qt. saucepan over medium-high heat to a boil. Stir pasta and chicken in saucepan. Reduce heat to medium. Cook 10 min. or until pasta is tender. Stir in onions and serve immediately.