1. Heat oil in a nonstick skillet over medium-high heat. Add onion, and cook 4 minutes or until onion is tender.
2. Combine onion, chicken, hot sauce, cream cheese, and 1 cup Cheddar cheese in a 2- or 3-qt. slow cooker.
3. Cover and cook on Low 2 1/2 hours. Remove lid; sprinkle top with remaining 1 cup Cheddar cheese. Cover and cook on Low 30 more minutes or until cheese melts. Serve with celery sticks.