Heat a little olive oil in a large casserole dish over a medium-high heat. Add the diced lamb and brown the pieces on all sides. Transfer to a plate.
Add the onion and garlic to the casserole and gently sauté until softened, adding a little more oil if needed.
Add the carrots, red pepper and sweet potatoes.
Stir in the Ras el Hanout, cumin, smoked paprika and tomato purée. Cook for a minute, stirring to coat the vegetables in the spices.
Return the lamb to the casserole and pour in the passata. Add enough water to generously cover the ingredients, then crumble in the stock cube and stir well.
Bring to the boil, then cover, reduce the heat and simmer gently for about 45 minutes, or until the lamb is tender and the sauce has thickened. Add a little more water during cooking if needed.
Stir in the chickpeas for the final 5–10 minutes to heat them through.
Taste and adjust the seasoning. Serve with chopped fresh mint or parsley and a squeeze of lemon juice.