Heat oven to 400 F degrees. Grease 2-quart casserole. Cook rice mixture following package directions.
Melt butter in large saucepan or skillet. Add onion; cook, stirring occasionally, until soft, about 5 minutes. Stir in flour, salt, pepper, half-and-half and broth; cook, stirring, to thicken, 5 minutes.
Add chicken, pimiento, parsley, nuts, rice. Spoon into casserole.
Bake, uncovered, in 400 degree F oven for 30 minutes. Makes 6 servings.