Place the chicken in a large bowl and set aside.
In a small bowl combine the mayonnaise, sour cream, and Dijon mustard. Mix well and set aside.
Add the celery, red onion, cheddar cheese, green onions, and bacon to the chicken.
Add the mayonnaise mixture to the chicken mixture and mix until well combined.
Sprinkle in the garlic powder, salt, and pepper, and mix well.
Refrigerate for at least 4 hours before serving.