In a saucepan, melt butter over medium heat. Stir in flour, salt, pepper, and onion powder until well blended.
Gradually stir in broth and milk, cooking and stirring until bubbly and thickened.
Stir in chicken and frozen vegetables. Remove from heat.
Place one pie crust in a pie dish. Pour the chicken mixture into the crust. Cover with the second pie crust, seal edges, and cut away excess dough. Make several small slits in the top crust to allow steam to escape.
Bake in preheated oven for 30-35 minutes, or until crust is golden brown and filling is bubbly. Let cool for 10 minutes before serving.