In a large nonstick skillet over medium heat, heat the canola oil. Add the potatoes and cook until lightly browned and crispy, about 10 minutes. Add the onions and pork, season with salt and pepper and cook until the onions and pork are heated through.
Preheat the oven broiler.
Spread the spicy brown mustard on one side of each slice of bread and place onto a baking sheet. Divide the sauteed pork between the 2 slices of bread. Sprinkle 2 tablespoons cheese over the top of each and broil until the cheese is melted and bubbling, about 2 minutes.
Garlic and Mustard Pork Roast:
Preheat the oven to 325 degrees F.
In a medium bowl, whisk together the mustard, canola oil, garlic, sugar and chopped rosemary. Place the pork roast on top of a rack fitted in a roasting pan. Place the 2 rosemary sprigs underneath the pork. Sprinkle the roast well with salt and pepper. Using a brush or hands, completely coat the roast with the mustard and garlic paste.
Place the roast in the oven and roast until the internal temperature reaches 145 degrees F, 2 1/2 to 3 hours. Remove from the oven, cover loosely with foil and allow to rest for 15 minutes before slicing.