Preheat the oven to 425°F (220°C).

Place frozen peas, carrots, and beans in a saucepan with celery; cover with water and bring to a boil. Reduce heat and simmer until celery is tender, about 8 minutes. Drain.

Melt butter in a saucepan over medium heat. Add diced onions and cook until translucent, about 5 minutes. Add flour, salt, pepper, celery seed, onion powder, and Italian seasoning; whisk until a paste forms, about 1 minute.

Slowly whisk in chicken broth and milk. Bring to a simmer and cook until sauce thickens, about 3 to 5 minutes.

Combine the thickened sauce with cooked vegetables and cubed turkey, stirring well.

Prepare two 9-inch pie dishes with a pastry crust at the bottom. Spoon half of the pot pie filling into each dish. Lay the remaining pastry dough over the top of each and seal the edges. Cut small slits in the top to vent.

Place the pies on baking sheets and bake in preheated oven for 15 minutes. Check for browning; if crust is browning too quickly, cover with aluminum foil. Continue baking until golden brown and filling is bubbly, about 20 more minutes.