Preheat the oven to 425°F (220°C).

Simmer frozen peas, carrots, green beans, and celery in a saucepan with water until tender, about 5 minutes. Drain.

Melt butter in a large saucepan over medium heat, add onion, and cook until translucent, about 5 minutes.

Add flour, salt, pepper, celery seed, onion powder, and Italian seasoning. Whisk to form a paste for about 1 minute.

Slowly whisk in chicken broth and milk. Simmer while whisking constantly until thickened, about 3-5 minutes. Remove from the heat.

Stir in cooked vegetables and cubed turkey into the sauce.

Fit pie crusts into the bottom of two 9-inch pie dishes.

Divide the pot pie filling evenly into both dishes and cover each with a top crust.

Seal and crimp the edges of the crusts. Cut small slits in the top crust for venting. Cover edges with foil or a pie shield.

Bake for 30 minutes, then uncover and bake for another 10-15 minutes until crusts turn golden brown and filling is bubbly.