Preheat oven to 375 degrees.
Lightly spray a skillet with cooking spray and cook chopped celery and onion over medium-high heat until softened. (About 5-7 minutes)
Spray a 3-quart or 9x13 casserole with cooking spray. Add celery and onions, raw chicken pieces, rice, condensed soup, ranch seasoning packet, buffalo sauce, and chicken broth. Stir together until combined well.
Cover casserole dish very tightly with aluminum foil to ensure proper cooking with the rice. (Use tin foil even if casserole dish has a lid, please!)
Place in preheated oven and cook for one hour or until rice is cooked.
Top with cheese, green onions, and extra hot sauce if desired. Enjoy!