Preheat oven to 375°F. Line a baking tray with parchment paper.
Remove pie shell from freezer if frozen. If refrigerated, add to pie tin. Defrost frozen vegetables and drain.
In a small frying pan, add oil and onion and cook on medium low heat until onion translucent (but not browned).
Meanwhile, mix together soup, milk, poultry seasoning, garlic powder, and pepper. Add vegetables, turkey, and onions and mix thoroughly.
Add to pie shell, place pot pie on the parchment lined baking tray, and bake for 30-40 minutes or until crust is browned and filling is bubbling. Allow to rest 5-10 minutes before serving.
Notes
Leftovers can be stored in an airtight container in the fridge for up to 4 days.