Start by cutting the pork loin into cubes and transfer everything to a large bowl.
Add the onions chopped into smaller pieces, the salt, a generous pinch of black pepper, a drizzle of olive oil and mix everything very well to combine.
Next, in a small bowl, add the mayonnaise, the unsweetened natural yogurt, the mustard seeds and mix everything very well until combined.
Now, add half of the meat we prepared into an oven bag.
Cover the meat with a medium potato, thinly sliced, 100g of grated mozzarella cheese, half of the sauce we prepared and spread it out.
Repeat this process with the remaining meat and attach the 2 bags to the oven rack.
Take them to a preheated oven at 180° C (350° F) and roast for 1 hour.
Serve.