Heat oven to 450ºF. Spread 1 tablespoon mustard over the entire loin; season with salt and pepper.
Place pork on rack in shallow roasting pan. Roast in 450ºF. oven for about 20 minutes until internal temperature reaches 150ºF. Let stand 10 minutes before thinly slicing.
Slice hoagie rolls in half horizontally and spread 1 tablespoon butter on the inside of both halves. Layer sandwich with the filling ingredients in the following order: sliced roast, sliced ham, remaining 4 tablespoons mustard, pickles and Swiss cheese.
Heat large skillet and coat pan with 1 tablespoon butter. Cook sandwiches in skillet until bread is golden brown and cheese is melted. (Can also use a sandwich press to grill.) Slice sandwiches in half diagonally and enjoy.