Preheat the oven to 375 degrees F. Melt butter in a large deep skillet over medium heat. Add the chicken-style strips and cook for 2-3 minutes, until heated through.
Stir in carrots and celery. Sprinkle with garlic powder, poultry seasoning, and 1/2 teaspoon black pepper. Continue cooking and stirring for 3 minutes, until vegetables are slightly tender.
Add peas and continue cooking for an additional 1 minute. Remove from heat and pour the mixture into a medium bowl.
In the same skillet used for the vegetables, heat the butter over medium heat. Add the onions and sauté for 1-2 minutes, until softened and fragrant. Stir in flour, salt, remaining 1/2 teaspoon black pepper, and celery seed. Gradually add the chicken broth and milk 1 cup at a time, stirring after each addition. Reduce heat to low and simmer for 3-5 minutes, stirring occasionally until thickened. Remove from heat.
Add the vegan chicken and vegetable mixture, stirring to coat.
Set one of the unbaked pie crusts on a rimmed baking sheet. Pour the filling into the crust.
On a floured surface, roll out the second pie crust and cut it into 3/4-inch wide strips. Arrange in a lattice pattern over the top of the pie. Use a knife to cut away the excess dough. Seal the edges by crimping them with your fingers or a fork. Use a knife to cut away any excess dough.
Bake for about 35 minutes, or according to pie crust directions, until the crust is lightly golden brown. Let the pie stand for at least 10 minutes to set and serve hot.