First of all, prepare the dough: in a bowl, work the sieved flour with water, oil, salt, and baking powder. Continue kneading until the dough is smooth and elastic.
Roll out the dough to a thickness of 4 mm on a floured pastry board and cut with a 10 cm diameter pastry pan. Fill the disks with a few Mozzarella STG cubes and half a slice of ham. Close the panzerotti and press firmly on the edges to close them.
Pour the peanut oil into a pot with high sides and bring it to 170 degrees, then fry a couple of panzerotti at a time. Drain the panzerotti and dry them on a sheet of absorbent paper. Serve them hot or warm.