Cut the mozzarella into slices. Wash tomatoes, dab dry and cut into slices. Roast pine nuts in a pan without fat, take them out. Wash the fish fillet and pat dry. Sprinkle with lemon juice and season with salt and pepper. Alternately cover with tomato and mozzarella, spread pesto on top and sprinkle with pine nuts. Cook in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 15-20 minutes