Cook the long-grain and wild rice mixes according to the package directions. Set aside.
2
Preheat the oven to 350 degrees F. Grease a 9-by-13-by-2-inch casserole dish.
3
In a large skillet, melt the butter. Add the mushrooms and onions and saute until the onions are translucent. Stir in the flour, cooking for 2 to 3 minutes. Slowly stir the broth into the onion mixture, then stir in the half-and-half. Cook until the mixture has thickened, 7 to 10 minutes.
4
Add the chicken, rice, salt, and pepper into the wet mixture.
5
Pour everything into the prepared casserole dish and bake, uncovered, until most of the liquid has been absorbed, 30 to 45 minutes.