It is very simple to make and we like it best on Italian prepackaged sliced bread (D'Italiano is the name brand I know, but they do have store brands too).
When I make my grilled pizza sandwiches or regular grilled cheese sandwiches I have found it easiest to butter the bread first, with two sandwiches each for hubby and I and one each for the girls it is just quicker. So I butter them, placing the butter sides in and piling the next one on and so forth.
Then I spread a tbs full of spaghetti sauce on the top slice of bread.
Then I add the shredded mozzarella cheese.
Then the pepperoni.
I then place the top slice of bread with all its toppings on the griddle.
Then I very carefully hold the bottom slice of bread (remember it has already been buttered) and I spread sauce on the unbuttered side.
And place it on the other slice sauce side down. I have been known to put it the wrong way when not paying attention, usually when I am in a hurry.
Brown on one side, flip, brown on the other.