Half of a recipe is really sufficient for the pie, so freeze the other half or just make half.
Top with mushroom sauce right before serving.
After adding the frozen veggies and chicken pieces, add three tablespoons flour dissolved in one and a half cups boiling water and continue cooking, stirring until thickened. Season with onion/mushroom soup mix and a bit of salt if desired. Disregard the remaining ingredients. Bake as above. This comes out just as good.