In a large bowl, whisk together the gluten free flour, xanthan gum, baking powder, salt, and garlic powder. Add the cold cubed butter and work it in with your fingers or a pastry cutter until the mixture resembles coarse crumbs. Add the eggs and cold water, then stir until a soft dough forms. Wrap in plastic and refrigerate for 30 minutes.
Preheat your oven to 375 degrees F and line a large baking sheet with parchment paper.
Divide the chilled dough into 6 equal portions. Roll each portion out between two sheets of parchment paper into a rectangle roughly 5 by 7 inches. The dough should be about 1/8 inch thick.
Spread about 1 heaping tablespoon of pizza sauce on one half of each dough rectangle, leaving a half-inch border around the edges. Layer 4 pepperoni slices and a generous 1/4 cup of shredded mozzarella on top of the sauce. Sprinkle lightly with italian seasoning.
Fold the empty half of the dough over the filling. Press the edges firmly with a fork to seal them completely. Transfer each pocket to the prepared baking sheet.
Brush the tops with beaten egg wash. Sprinkle each one with a little grated parmesan and italian seasoning. Use a fork to poke 3 small vent holes in the top of each pocket.
Bake for 22 to 25 minutes until the tops are golden brown and the dough is fully cooked through. Let them cool for at least 5 minutes before eating because the filling will be extremely hot.