Wash the pork tenderloin, dab dry and cut into 1 1/2 - 2 cm thick medallions. Heat the oil in a pan and fry the medallions (possibly in 2 portions) while turning.
Season with salt and pepper and remove from the pan. Wash the tomatoes, dab dry and cut into thick slices. Drain the mozzarella and also cut into slices. Wash basil, dab dry and pluck off the leaves, except for a little to garnish.
Grease a gratin dish and layer the medallions, tomato and mozzarella slices in a fan shape in the dish. Place 3/4 of the basil leaves between the slices. Drizzle the gratin with olive oil and sprinkle with salt and pepper.
Bake in a preheated oven (electric range: 250 °C/ gas: level 5/ convection oven: 225 °C) for 10-15 minutes. Sprinkle with remaining basil and garnish. Serve with fresh ciabatta bread.