Kousa Mashi Bil Laban (Lamb Stuffed Zucchini in Yoghurt Sauce)

Ingredients

• 24 small, fat zucchini
• 1/2 pound ground lamb
• 2 teaspoons allspice
• 1 teaspoon dried mint, plus more to serve
• 3 tablespoons toasted pine nuts
• 1 head garlic, finely minced, divided
• olive oil
• 2 pounds yoghurt, preferably sheep's milk
• 1 tablespoon cornstarch mixed with 2 tablespoons water