You can use a 4-ounce can of mushroom pieces and stems, drained, instead of the fresh mushrooms. Add the mushroom liquid with the milk in step 2 for a mightier mushroom flavor.
Why not turn to tuna? Tuna à la King is as easy as replacing the chicken with a 12 1/2-ounce can of drained tuna.
Make your chicken fit for a king! Serve it over toasted bread triangles, as shown, instead of rice.