Cut the fillets in 2, but not all the way through. Salt and sprinkle them with black pepper on both sides. Sprinkle the oven dish with half the olive oil and put the fillets in it.
Distribute the tomato paste over the fillets, as well as the mozzarella, cut into strips.
Finally, add the finely diced cheese cubes and the rest of the olive oil. Sprinkle with basil.
Bake at 392°F (200 °C), covered with foil for the first 30 min. and 20 min. without it, to crisp the cheese.