1. Preheat your oven to 350°F (180°C).
2. Peel, wash, and finely chop the onion.
3. Wash, then slice the zucchini in half lengthwise.
4. Then, hollow out the zucchini and remove the seeds.
5. Take a gratin dish, grease it, and add a small amount of water so that the mixture does not stick during cooking.
6. Place the zucchini in the dish, then season with salt and pepper.
7. Take a frying pan, grease it, heat it up, and brown the onion and ground meat.
8. Add the peeled tomatoes, cut into large cubes, to the mixture in the frying pan.
Season with salt, pepper, and herbs.
9. Fill the zucchini with the mixture, then sprinkle with grated gruyère cheese.
Bake for 30 minutes.
10. 15 minutes before the end of cooking, prepare the rice.