Combine 1/2 cup yoghurt with spices and garlic in a shallow container, stir through lamb until coated. Cover and refrigerate for at least 30-minutes.
Heat the oil in a large non-stick saucepan and gently cook 3/4 of the onion for 5 minutes or until tender and lightly browned. Reserve remaining onion for serving.
Add the lamb to the pan and cook over medium heat for 5-8 minutes or until browned. Add the stock and chickpeas, bring to the boil, cover and simmer for 1 hour or until the lamb is tender. Remove lid and simmer for a further 4-5 minutes or until the sauce is reduced and sticky.
To serve, spoon lamb into a serving bowl, top with reserved onion, dollops of remaining yoghurt and coriander. Dip the cut side of each date in sesame seeds and arrange over the tagine. Serve accompanied with carrots and couscous.