Preheat oven to 425 degrees F and spray a 9-inch pie plate with cooking spray lightly.
Heat 1 Tablespoon oil over medium high heat in a large skillet. While heating, sprinkle the salt and pepper over your beef chunks.
Cook half of your beef at a time browning each side of the beef cubes, about 30 seconds per side. The meat doesn’t need to be fully cooked.
Remove to a plate and add 1 more tablespoon of oil to the skillet and heat, cooking the second half of the meat.
Reduce the heat to medium and add the last Tablespoon of oil and add the onions and potatoes to the skillet. Cook until potatoes are mostly tender, about 8 minutes. They will continue cooking in the oven, so they don’t need to be fully cooked.
Add the thawed mixed vegetables and heat 1 minute before removing the vegetables to a different bowl.
To the same skillet make the gravy by first adding the butter. Once melted, add the flour and whisk for about 4-5 minutes.
Add the beef broth while mixing followed by the milk, Worcestershire sauce, salt, pepper, and garlic powder.
Cook until the gravy is thickened, about 5-7 minutes. Add more salt and pepper to taste.
Add the cooked meat and veggies to the sauce and mix.
To your prepared pie pan, lay the first pie crust down and prick with a fork. Pour the mixture inside.
Lay the 2nd pie crust over top and crimp the edges together to seal the 2 crusts with a fork or pressing with your fingers.
Make the egg wash by whisking the egg and water together.
Evenly brush a layer of egg wash over the top and make a few slits on the top crust to allow steam to escape.
Bake for about 25-35 minutes until the filling is bubbling and the crust is golden brown. Check the pie at about 25 minutes and cover the top with foil if the edges are getting too brown and the inside isn’t bubbling through the slits yet. Do not bake less than 25 minutes or you risk having the bottom dough be not cooked through.
Remove from oven and let the pie cool for 20 minutes before slicing and serving.