Press the pie crust into the bottom of a 9x13-inch baking dish, then layer the turkey meat over the crust; spoon the cream of chicken soup over the turkey.
Bring 1 cup of water to a boil in a saucepan over medium heat, and stir in the mixed vegetables; cook until the vegetables are tender, about 5 minutes. Whisk the dry gravy mix with the remaining 1 cup of water, then stir the gravy mixture into the mixed vegetables. Bring to a boil, then simmer until thickened, about 1 minute. Pour the vegetables and gravy over the cream of chicken soup layer in the pan. Spread the mashed potatoes over the top of the pie.
Bake in the preheated oven until the filling is bubbling, about 45 minutes.
