Preheat oven to 375°F. Cut each square of dough into 6 same sized rectangles. Avoiding around ½” around each edge, layer mustard, ham, and cheese on half of the rectangles.
Using a pastry brush, add beaten egg to the edges of the top and bottom piece of the dough so they will form a seal. Invert the top rectangle on top of the other side that has the filling. Use a fork to press around all the edges to form a tight seal.
Cover each pocket sandwich with more egg wash and cut two slits on top to vent. Bake in preheated oven for 15-20 minutes. Enjoy hot or pack in lunches for the little ones to eat cold or reheat at school!