In a deep, 8 inch heavy-bottomed skillet, heat the olive oil over medium heat. Season the chicken breasts with salt and pepper and add to the skillet.
Cook the chicken until done and no longer pink in the center, approximately 6 minutes each side. Transfer to a plate and allow to rest until cool enough to handle.
Cut the chicken into bite sized pieces and set aside. (This can be done while the vegetables are cooking.)
Whisk together the cornstarch and half and half. Set aside.
Add the carrots and onion to the skillet. Saute over medium heat until the vegetables have softened. Add the celery and continue to cook until softened. Stir in the garlic and cook for one minute. Add the garlic powder, nutmeg, thyme and stock to the pan stirring to combine.
Slowly add the half and half continuing to stir until all the ingredients are thoroughly combined. Stir in the chicken and cook until the mixture begins to thicken, approximately 5 minutes. Turn off the heat and season with salt and pepper to taste.
Roll out one refrigerated pie crust and top the filling with the crust. Using your fingers, press the crust down along the sides of the skillet allowing the edges to face up towards the top of the skillet. Using a knife, cut two 1 inch slits in the center of the crust.
Bake the pot pie for 15-20 minutes or until the crust is golden brown. Serve immediately.