Cut the pork meat into slices about 1/2″ (1.5 cm) thick but not all the way through - leave them attached at the bottom.
For the marinade, mix together the mustard, olive oil, lemon juice and soy sauce in a bowl. Stir well to obtain a homogeneous mixture and smear the meat generously with it on all sides using a brush, including in between the slices. Wrap the meat tightly with plastic wrap and leave it for 10 hours in the fridge.
After it's sat in the fridge for the full duration, take out and prepare the other products. Wash the tomatoes and mushrooms, cut them into slices 1/4 (5 mm) thick. Cut the smoked cheese to the same thickness. Peel the garlic cloves and cut them into thin slices.
Lay out a large sheet of aluminum foil in a tray and transfer the meat in the middle of it. In each incision, put a slice of cheese, slice of tomato, 2 slices mushrooms and 4-5 garlic clove slices in between those.
Wrap the meat tightly with the foil, like a packet, and bake in a preheated 392°F (200 °C) oven on the middle element about 50 min. with the fan on.
Serve the ready dish sprinkled generously with finely chopped fresh parsley.