Combine the onion, garlic, oregano, lemon zest and juice and olive oil in a food processor and blend until smooth. Massage the mixture all over the lamb shoulder and season well. Cover, refrigerate and leave to marinate for at least 2 hours, or overnight.

Preheat oven to 200°C fan-forced (220°C conventional).

Place the shoulder in a roasting tin, skin-side up, then roast for 10 minutes to caramelise. After 10 minutes, add the wine to the tin, cover with baking paper, then aluminium foil to seal the edges, and reduce the temperature to 150°C fan-forced (170°C conventional). Roast for 2 hours.

Strain the soaked chickpeas and add to the tin around the lamb, covering again with baking paper and foil, and adding a little water, if necessary, to almost cover the chickpeas. The chickpeas will begin to cook along with the lamb and absorb the cooking juices. Continue cooking the lamb for a further 2 hours or until tender. For the final 15 minutes of cooking, increase the oven temperature to 200°C fan-forced (220°C conventional). Remove the foil, add the tomatoes and mint to the pan, mixing slightly with the chickpeas, and cook uncovered.

Remove from the oven and allow to rest for 10 minutes, skim some fat from the pan then serve.