Rinse the zucchini, cut in half lengthways, remove the seeds. Preheat the oven to 180 ° C. Peel and chop the onion and garlic and sauté in the oil. Add tomato paste, pieces and raw pasta. With the lid on, simmer for 10 minutes. Pick up the tuna, fold in, season with salt and pepper. Grease a baking sheet. Place the zucchini halves on top and fill with the tuna mixture. Sprinkle grated cheese on each zucchini half. Bake for about 25 minutes. Garnish with salad if necessary.