Add the marinara sauce to the griddle and grill the sauce for 15-20 seconds, mixing with a spatula every few seconds. Add the meat back to the griddle and combine it with the sauce. Turn the griddle off and use spatulas to shape the meat into a cylinder shape the same length as the loaf of bread. Add the sliced mozzarella to the sauced meat and close the griddle lid for 2-3 minutes.