Preheat the oven to 425 degrees F (220 degrees C).
Add celery, frozen peas, carrots, and beans to a saucepan with enough water to cover and boil. Simmer 8 minutes over medium-low heat until celery is tender. Drain.
While vegetables simmer, melt butter in a saucepan over medium heat. Add onion and simmer 5 minutes until transparent.
Whisk flour, salt, pepper, celery seed, onion powder, and Italian seasoning for 1 minute to make a paste. Slowly whisk in chicken broth and milk until combined; boil, stirring frequently, until sauce thickens, 3–5 minutes.
Remove thickened sauce from heat; whisk in cooked, drained veggies and cubed turkey until incorporated.
Prepare two 9-inch pie dishes. Bottom each dish with a pie pastry. Place 1/2 of the pot pie filling in each dish and top with remaining pie pastry.
Seal the top and bottom pastries by pinching and rolling. Cut numerous small incisions in each top pastry with a sharp knife to vent steam while cooking. Pies on baking sheets.
Bake for 15 minutes in preheated oven. Cover the top crusts with aluminum foil if they brown too rapidly. Bake 15–20 minutes more until the crusts are golden brown and the filling is bubbling.