Pat the lamb leg dry and season with sea salt and black pepper.
Heat olive oil in a heavy-bottomed pot over medium heat and sear the lamb until browned on all sides.
Add the diced onion, minced garlic, and grated ginger to the pot, sautéing until the onion is translucent and fragrant.
Stir in the cumin, coriander, cinnamon, and turmeric, coating the meat and vegetables in the spice blend.
Pour in the vegetable broth and add the sliced carrots, diced zucchini, and rinsed chickpeas.
Reduce heat to low, cover, and simmer for 45-60 minutes until the lamb is tender.
While the tagine simmers, prepare the couscous by pouring boiling water over the dry grains in a bowl, covering, and letting it sit for 5 minutes.
Fluff the couscous with a fork and serve the lamb tagine over the grains, garnished with fresh cilantro.