Heat the olive oil in a heavy-bottomed pot over medium-high heat.
Add the cubed lamb shoulder and sear until browned on all sides, then remove and set aside.
In the same pot, sauté the diced onion and carrots for 5 minutes until slightly softened.
Stir in the tomato paste, cumin, coriander, cinnamon, salt, and pepper, cooking for 1 minute until fragrant.
Return the lamb to the pot along with the chickpeas and beef broth, bringing the mixture to a gentle simmer.
Cover and cook on low heat for 45 minutes or until the lamb is tender and the sauce has thickened.
While the lamb simmers, place the dry couscous in a small bowl and pour the boiling water over it.
Cover the couscous bowl and let it sit for 5 minutes, then fluff with a fork.
Serve the lamb tagine over the couscous and garnish with fresh chopped cilantro.