Cook and shred your chicken.
Preheat the oven to 425° F. Press one of the pie crusts into a 9" pie plate and set aside.
In a medium saucepan, over medium heat, melt the butter. Add the chopped onion and cook for about 2 minutes until tender.
Whisk in the flour, salt, pepper, and poultry seasoning. Cook until the mixture thickens.
Gradually stir in the milk and chicken broth, cooking until thick and bubbly.
Stir in the shredded chicken and thawed mixed veggies, then remove from heat.
Pour the mixture into the prepared pie crust and top with the second crust. Seal edges and cut several slits in the top crust.
Bake for 30-40 minutes until golden brown, covering crust edges with foil during last 15-20 minutes to prevent burning.
Let the pie stand for 5 minutes before slicing and serving.
