Paula Deen's Chicken and Rice Casserole

I first had this at the Paula Deen buffet in Tunica and loved it. I had to find the recipe, so here it is:

1 onion, diced
2 T olive oil
3 c. chicken, cooked and diced
6 oz. box long-grain wild rice, cooked according to box
1 can water chestnuts, diced
2 cans green beans
1 4 oz can pimentos
1 can cream of celery
1 c. mayonnaise
1 c. cheddar cheese
salt to taste

Saute onion in olive oil until transparent. Mix all other ingredients together in big bowl. Bake at 375 degrees for about 25 minutes until hot and bubbly.