Bring a large pot of salted water to a boil and cook the zucchini until just tender.Drain them well. Cut each zucchini in half lengthwise and carefully scoop out the flesh with a spoon, leaving a thin shell intact (Photo 1).Place the zucchini flesh into a sieve (Photo 2) and squeeze out as much liquid as possible (Photo 3).
Finely chop the leek (or onion) and sauté it gently in olive oil until soft (Photo 4).Add the squeezed zucchini flesh to the pan and cook for a few minutes to evaporate any remaining moisture. Finely grate the Parmesan cheese (Photo 5) and prepare fresh breadcrumbs from stale bread (Photo 6).
In a large bowl combine: ground meat, cooked zucchini, flesh grated Parmesan, breadcrumbs (Photo 7). Add the egg, salt and a pinch of freshly grated nutmeg. If you like, season with freshly ground black pepper. Mix everything well until you obtain a uniform filling.
Fill each zucchini shell generously with the mixture (Photo 9).Grease a baking dish with olive oil and arrange the stuffed zucchini inside (Photo 10).Mix equal parts grated Parmesan and breadcrumbs (Photo 11) and sprinkle the mixture over the zucchini (Photo 12).
Drizzle with 2–3 tablespoons of extra virgin olive oil (Photo 13).Bake in a preheated oven at 180–200°C (350–390°F) for 30–40 minutes, or until the tops are beautifully golden brown (Photo 14).
Let the zucchini cool for a few minutes before serving.Enjoy them warm, at room temperature or even cold the next day.