Cook the long-grain and wild rice mixes according to the package directions. Set aside.
Preheat the oven to 350 degrees F. Grease a 9-by-13-by-2-inch casserole dish.
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 (and reserved canned mushroom liquid if using) into the onion mixture, then stir in the half-and-half. Cook until the mixture has thickened, 7 to 10 minutes.
Add the chicken, rice, toasted almonds, pimientos, parsley, salt and pepper into the wet mixture. Pour everything into the prepared casserole dish and bake, uncovered, until most of the liquid has been absorbed, 30 to 45 minutes.