Prepare the vegan pie crust and chill it for at least an hour. I make the dough the night before and let it sit in the fridge overnight. The pie crust recipe makes 2 crusts. We'll use both in this recipe.
Prepare the vegan chicken. Make sure the vegan chicken is thawed, then cut it into bite-size pieces. Some vegan chicken will need to be cooked in a skillet, so it's not mushy.
Cook the butter and onions in a large skillet over medium heat. Stir occasionally and cook the onions until tender, around 5 minutes. Then add the garlic and cook for another minute.
In a bowl, stir together the flour, salt, and spices. Stir this into the butter mixture along with the broth, and soy milk. Cook and stir until you've worked out the lumps in the mixture.
Add the potato cubes, turn the heat down to medium-low, and simmer (low boil), for 10 to 15 minutes, until it resembles a thick gravy.
Add the frozen vegetables and chopped vegan chicken and stir it all together. Remove the skillet from heat and set it aside to cool.
To begin baking the pie, preheat the oven to 400°F/200°C.
Remove one of the chilled dough discs from the fridge. Lightly flour a work surface or use a rolling mat. Use a rolling pin to roll out the dough disc until you have a circle approximately 12 inches in diameter. Gently transfer the rolled dough into a 9-inch pie pan. Roll the second dough dish until it's approximately a 12-inch circle.
Spoon the gravy mixture into the pie. Cover the pie with the top crust. Trim any excess dough around the sides, and then pinch the edges with your fingers to seal it. Then add fork marks. Use a paring knife to add slits in the top crust. This allows steam to escape, so you'll need only a few.
Stir together the vegan egg wash ingredients. Dip a pastry brush in the wash and brush it over the top crust and edges.
Place the pie pan on a baking sheet in the oven. Bake for 35 to 40 minutes until the crust is golden brown. After around 20 minutes of baking, add a pie crust shield to keep the edges from getting too brown. Remove it from the oven and allow it to cool for 15 minutes before serving.
Store in an airtight container in the fridge for up to 5 days.