Preheat the oven to 400 degrees, and remove the pie crusts and cream cheese from the refrigerator.
Slice your onion and mushrooms.
Meanwhile, add the butter to a large skillet and heat it over medium heat until melted and starting to bubble. Swirl to coat the pan, then add the onion and saute for five minutes, stirring occasionally.
Add the mushrooms and garlic and continue to saute over medium heat for another nine minutes, stirring occasionally, or until the mushrooms and onions are browned and softened.
While the veggies are sauteing, shred the mozzarella (if not using pre-shredded) and chop the cream cheese into small chunks. Unroll the pie crusts and cut each into three equal triangles, for a total of six pieces.
Stir the chicken, mozzarella, cream cheese, and spices into the pan with the onions & mushrooms. Continue to stir until the cheese is melted and well incorporated throughout, then turn off the heat under the pan.
Spoon equal amounts of the cheesy chicken, mushroom, & onion mixture into the center of each of the pie crust wedges. Fold the crust over the filling and crimp the edges with your fingers.
Arrange the hand pies on a rimmed baking sheet. Beat one egg with 1 tsp water to make an egg wash. Brush each hand pie with the egg wash, and optionally cut a couple of small slits in the top of each to let steam escape.
Bake for 20 minutes at 400 degrees, or until hand pies are golden brown.
Be careful if eating these right out of the oven; the filling will be molten hot.
Leftover Chicken, Mushroom, & Mozzarella Hand Pies from Mashup Mom: https://www.mashupmom.com/leftover-chicken-mushroom-mozzarella-hand-pies/