Mash garlic and salt together; mix with orange juice, lemon juice, onion, oregano, and olive oil. Using a sharp knife or a fork, pierce pork all over and place in marinade (reserve 1/4 cup/50 mL for basting), coating the pork thoroughly. Marinate refrigerated overnight.
Preheat oven to 450°F (230°C). Drain off marinade; discard. Place pork in an open roasting pan and roast for 10 minutes. Reduce heat to 325°F (160°C). Baste occasionally with reserved marinade. Remove roast when internal temperature reaches 155°F (68°C) using a meat thermometer, about one hour total roasting time. Allow to cool and reserve any meat juices for sandwich. Tent loosely with foil and allow to cool, reserving any meat juices for sandwich.
To assemble sandwich: Cut bread in half lengthwise and butter both sides. Pre-heat oven to 350°F (180°C). Fill sandwich by placing layers of sliced pickles, sliced roasted pork (be generous), ham, and cheese. Replace top to make a sandwich and cut diagonally into eight portions. Put all on a baking sheet with a heavy skillet on top to compress. Place in oven until cheese melts, about 25 minutes. Serve with mustard and mayonnaise, salt and pepper to taste.