Preheat the oven to 425ºF and make sure the pie crusts are thawed. Line a 9-inch pie pan with one of the crusts.
Heat the olive oil in a large pot over medium/high heat. Add the onions and season with ¼ teaspoon of salt. Saue the onion for 4-5 minutes.
Add the mushrooms to the pot and season them with another ¼ teaspoon of salt. Saute them for an additional 4-5 minutes until the mushrooms are cooked down and any excess liquid is cooked off. Add the garlic and saute for an additional minute. Transfer the vegetable mixture to a bowl and set aside.
In the same pot, melt the butter over medium heat. When the butter is melted add the flour and dried thyme and whisk the ingredients together. Cook them for about 1 minute.
Slowly add broth and milk to the pot and whisk the mixture until it begins to thicken.
Once thickened, remove the pot from the heat. Add the black pepper, turkey, cooked vegetables, the remaining salt, and the thawed frozen vegetables. Mix until all of the ingredients are coated in the roux.
Transfer the mixture to the pie crust. Carefully top the vegetables with the second pie crust. Pinch the edges of the pie together to secure the filling. Cut off any additional pie dough from the edges. Discard or roll out the crust and use the additional pie crust to create a design for the top of the pie.*
Place the pie in the oven and bake for 40-50 minutes. Place a baking sheet on the shelf below to catch any bubbly overflow. Check the pie halfway through the baking time. If the top of the pie is already browning halfway through, cover the pie with tin foil and continue to bake. The pie is done when there is a bit of bubbling over the edges.
Remove from the oven and let it rest for 10-15 minutes.