Trim any excess fat from the lamb leg and cut into 1-inch cubes.
Heat the olive oil in a heavy-bottomed pot or tagine over medium heat and brown the lamb on all sides.
Add the diced yellow onion and sliced carrot to the pot, sautéing for 3-4 minutes until the onion is translucent.
Stir in the tomato paste, cumin, coriander, cinnamon, ginger, sea salt, and black pepper, coating the meat and vegetables evenly.
Pour in the beef broth and add the chickpeas, then bring the mixture to a gentle boil.
Reduce the heat to low, cover, and simmer for 35-40 minutes until the lamb is tender.
Add the sliced zucchini during the last 10 minutes of cooking to ensure it stays tender-crisp.
While the tagine simmers, prepare the whole wheat couscous by combining it with 0.25 cup of boiling water in a covered bowl for 5 minutes, then fluff with a fork.
Serve the lamb tagine over the fluffy couscous and garnish with freshly chopped cilantro.