01Slice half an inch from each end of the zucchini and carefully remove the insides by inserting a corer and twisting; repeat until the zucchini is hollow. Repeat for all 15 zucchini, then set aside.
02In a large bowl, mix rice, meat, half of the onion, herbs, and spices for filling.
03Stuff zucchini with filling, leaving a half-inch of space at the ends.
04Layer stuffed zucchini horizontally in a large pot. Place a heavy plate on top of the zucchini to prevent them from floating and losing their filling.
05Pour broth over zucchini. If needed, add water until liquid reaches the plate and zucchini are entirely submerged. Bring broth to a boil and gently simmer on medium low heat for 30 minutes.
06Remove plate and zucchini from broth and set aside; keep broth.
07In a large saucepan, on medium heat sauté remaining onion and garlic until fragrant and translucent. Add 3 cups of broth and bring to a simmer.
08Carefully temper yogurt into the broth: With the yogurt in a large bowl, pour 1 ladle of hot broth into yogurt and stir until combined. Repeat three times. This prevents the yogurt from curdling when you add it to the broth.
09Pour yogurt mixture into broth.
10Mix water and cornstarch and stir into yogurt sauce over medium heat. Stir until the sauce thickens and begins to bubble. Remove from heat.
11Plate zucchini in a deep platter, generously coat with yogurt stew, and garnish with pine nuts.
12Serve warm in large soup bowls to accommodate sauce.