To make the filling for the chicken pot pie, start by melting the butter in a saucepan over medium heat. Once the butter has melted, add the flour, salt, black pepper, onion powder, garlic powder, thyme, and parsley. Make a thick paste by stirring the mixture.

Next, gradually add the chicken broth and milk, stirring constantly, until the sauce thickens. Add the cooked chicken and mixed vegetables, and stir until they are well coated with the sauce.

Preheat your oven to 375 degrees Fahrenheit. Transfer the filling to a pie dish, and top with the pie crust. Use a fork to crimp the edges of the crust, and make a few small slits in the top of the crust to allow steam to escape.

Bake the chicken pot pie for 30-35 minutes, or until the crust is golden brown and the filling is hot and bubbly. Before serving, let the pie cool for a few minutes. Serve hot, and enjoy!