Preheat oven to 375 °F (190.5 C) and coat a baking dish with nonstick spray.
In a large bowl stir together celery, sour cream, mayo, and cream of chicken. Fold in the chicken. Spoon into the baking dish.
Bake uncovered until the chicken reaches an internal temperature of 155 degrees using a thermometer, about 20 to 30 minutes.
Switch the oven to broil.
Top with cheese and fried onions, and broil until golden brown, about 5 minutes. Let stand for 5-10 minutes.
Place green beans in a skillet and cover with 1/2 cup water over medium-high heat. Cover with a lid and cook for 3-5 minutes. Remove the lid and let the water evaporate until they are soft and tender. Season with salt and pepper to taste.
Toast the bread, then spread it with butter.
Serve the casserole with green beans, bread, and sparkling water.