Cook the bacon in a skillet over medium heat until it’s released its fat. Add the garlic and chopped mushrooms and cook for about 10 minutes, or until the mushrooms have released most of their moisture. Add the chopped spinach and cook it until it’s thawed. Add the tomato sauce and salt and stir to combine. Remove the mushroom filling from the pan to cool.
Unroll both pie dough rounds and, using a pizza cutter, cut each into 4 triangles. Divide the mushroom filling between each triangle, placing the filling in a pile just off-center on the dough. Top with some mozzarella and Parmesan cheese. Moisten the edges of the pie with a little water (I find using my finger to do this works best). Fold the dough over the filling and seal the edges by gently pressing them together.
Cut a few slits in the top of each hand pie to allow steam to escape as they bake. Brush the tops of the hand pies with a light coating of the beaten egg. Sprinkle the remaining 1 tbsp of Parmesan cheese over the top. Bake at 350 degrees for 20-30 minutes, or until the hand pies are golden brown. Cool the hand pies for a few minutes before serving.