Preheat oven to 425°F (220°C).
In a saucepan, melt butter over medium heat. Add onions and cook until tender.
Stir in flour, salt, pepper, onion powder, and garlic powder until well blended.
Gradually stir in chicken broth and milk, cooking and stirring until bubbly and thickened.
Stir in chicken and mixed 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 slits in the top for steam to escape.
Bake for 30-35 minutes, or until the crust is golden brown. Let cool for 10 minutes before serving.