Cut bread halves lengthwise, cutting to but not through opposite side. Spread mustard on cut sides of bread. Layer with Baked Pork Loin Roast and next 3 ingredients. Close sandwiches, and spread outsides with butter.
Place 1 sandwich in a hot, large skillet over medium heat. Place a heavy skillet on top of sandwich. Cook 2 to 3 minutes on each side or until cheese is melted and sandwich is flat. Repeat with remaining sandwich. Cut each sandwich in half, and serve immediately.
*1/3 lb. thinly sliced Slow-Cooker Pork Butt Roast may be substituted.