For the lamb, mix all the ingredients, apart from the lamb, in a shallow non-reactive dish. Score the rumps with a sharp knife and rub the mixture all over the rumps. Leave in the dish, covered, to marinate for at least two hours in a cool place.
Preheat the oven to 200C/390F/Gas 6.
Brown the lamb well in a hot frying pan, before placing in the oven to roast for 15-20 minutes – longer if you prefer your meat well done.
Leave to rest in a warm place for at least five minutes before serving.
Meanwhile, for the vegetable stew, heat the oil in a pan over medium heat and fry the bay leaves, cardamom pods and garlic cloves for one minute.
Add the onions and fry until lightly coloured. Stir in the ginger and garlic paste and cook for a further two minutes, until fragrant.
Add the coriander, chilli powder, cumin, turmeric, salt, tomatoes, potato, turnips and carrots. Stir well and simmer for 30 minutes.
Once the potatoes and other vegetables are tender when tested with the point of a knife, add the drained chickpeas. Cook for a further five minutes.
Scatter the coriander over the stew and serve it topped with the lamb rump.