Preheat oven to 425°F.
Place one pie crust in the bottom of a 9-inch pie plate.
In a large bowl, combine the chicken, cooked vegetables, and season to taste. Set aside.
In a saucepan over medium heat, cook the onions in the butter until soft and translucent.
Stir in the flour, salt and pepper. Slowly stir in chicken broth and milk.
Simmer over medium-low heat until thick. Remove from heat, pour over the chicken and vegetables and mix well.
Pour mixture into the prepared pie shell and add top crust.
Cut away any excess dough and seal the edges. Make several small slits in the top to allow steam to escape.
Bake in the preheated oven for 30 to 35 minutes, or until pastry is golden brown and filling is bubbly.
Cool for 10 minutes before serving.
