Place all of the ingredients in the crockpot (besides the Bell Peppers and Celery). Cover and cook on low for 6-8 hours or on high for 3 hours.
Shred the chicken directly in the crockpot to your desired texture. Add in Bell Peppers and Celery.
Cover and cook on high for another 30-45 minutes. (This is a great time to make your rice!)
Serve the gumbo over rice and top with green onions.