Cook wild rice according to package directions with the addition of a bay leaf. Once done, discard bay leaf and set rice aside until ready to use.
Toss crushed Ritz crackers with olive oil and set aside until ready to use.
Preheat oven to 350° F. Prepare a 9x13 baking dish with cooking spray or a thin layer of softened butter.
To a large skillet, add butter over medium-high heat. Once melted add green onions and celery then cook until softened.
Sprinkle flour over vegetables then stir to combine well. Continue cooking for 1-2 minutes. Slowly whisk in half and half then chicken broth. Add thyme, nutmeg, salt and pepper.
Continue cooking and stirring until thickened, about 3-5 minutes. Add half of the shredded cheese, chicken and cooked wild rice. Stir to combine well. Pour into prepared baking dish. Top with remaining cheese.
Place in oven and bake for 20 minutes. Remove from oven and sprinkle Ritz crackers evenly over casserole. Return to oven and bake for 15 more minutes or until golden brown.