Peel, wash and halve the potatoes. Cook in boiling salted water for about 20 minutes. Wash the chives and, except for a little bit for garnishing, cut into fine rolls. Wash the meat and dab dry.
Heat the oil in a frying pan. Fry the meat for about 3 minutes on each side, place on a baking tray. Place 1 slice of pineapple and 1 slice of cheese on each slice of pork loin. Bake under the preheated grill for 3-4 minutes.
Meanwhile drain the potatoes. Warm the milk, add it to the potatoes and mash it to puree, season with salt, pepper and nutmeg. Stir in the fat and chive rolls. Put 1-2 tablespoons of mashed potatoes on each plate and arrange the gratinated meat on top.
Garnish with chives.