Heat a knob of butter in a frying pan and, once melted, add the roast pork (or roast ham). Fry, stirring often, until browned.
Roast pork works especially well for Cuban sandwiches, but if you don't have any roast meat, don't worry, you can substitute it with pretty much whatever pork cold cuts you have on hand, or easily available in your area.
Cut the bread loaves in half and spread one half of each loaf with mustard generously. Add the browned pork on top, then the sliced pickles and the Swiss cheese.
Place the other half of each loaf on top and brush the outsides of the sandwich with butter. This will prevent the bread from sticking to the sandwich maker (or frying pan).
Place your sandwiches in the heated sandwich maker one at a time until the cheese has melted and the bread has toasted but not burned. You can use a frying pan instead, if you don't have a sandwich maker, just make sure to press down on the sandwich with a slotted spoon to grill the bread properly on both sides and so the filling heats up enough to melt the cheese.
Once nicely golden, you can take off from the heat. Enjoy!