Preheat your oven to 350 degrees Fahrenheit. This is an essential step to ensure your casserole cooks evenly.
Lightly grease either a 7 by 11-inch or a 9 by 13-inch casserole dish. This will keep your casserole from sticking and make for easier cleanup.
In a large mixing bowl, combine all the ingredients: the diced, cooked chicken, white and wild rice, cream of celery soup, chopped pimentos, finely chopped onion, mayonnaise, French-style green beans, sliced water chestnuts, black pepper, and salt. Mix everything well until fully incorporated.
Once mixed, taste the mixture, and adjust the salt if necessary. This step is important to achieve the desired flavor.
Transfer the mixture to your prepared baking dish. Spread it evenly to ensure even cooking.
Place the casserole in the preheated oven and bake for 25 to 30 minutes uncovered. You’ll know it’s ready when the top is golden brown and bubbly.
Once baked, remove the casserole from the oven and allow it to cool slightly. This resting time helps the casserole set up, making it easier to serve.
Cut into squares and serve warm. Enjoy each bite of this hearty dish, and don’t forget to savor the leftovers!
