Preheat the oven to 370°F. Cut each zucchini in half lengthwise and scoop out the flesh with a spoon. Chop the zucchini flesh in small chunks and set aside.
Place the scooped out zucchinis in the oven and cover with tin foil. Bake for 20 minutes or until tender when pierced with a fork.
Meanwhile, cook the rice, drain and set aside.
In a large frying pan, add olive oil and sauté the lamb over medium heat until browned. Add the zucchini flesh, the chopped onion, nomato sauce, mint, garlic and rosemary. Stir in and let simmer for 10 minutes. Salt to taste.
Remove the frying pan from heat and mix well together the stuffing with the rice.
Fill your zucchini boats with the stuffing. Sprinkle with shredded mozzarella cheese.
Bake for 15–20 minutes until cheese is melted and zucchinis are cooked through.