Step 1

Preheat the oven to 170C/150C Fan/Gas 3.

Step 2

To make the spice mix, tip all the spices into a clean, medium-sized airtight container, cover with the lid and shake. Set aside.

Step 3

To make the lamb, put the olive oil and lemon zest and juice in a bowl, add 4 tablespoons of the spice mix and mix well.

Step 4

Put the onion quarters in a medium, deep-sided roasting tray and place the lamb on top (you want it to fit snugly so don’t use a roasting tray that is too big). Make several incisions in the lamb. Spread the spice mixture all over the lamb, rubbing it into the incisions well. Pour 300ml cold water into the bottom of the tray, then cover the whole thing with kitchen foil. Roast for 3¼ hours, or until the meat is tender and falling off the bone.

Step 5

Meanwhile, prepare the couscous. Tip the couscous into a large, heatproof bowl, add the lemon zest and juice, then pour in the boiling water and stir well. Cover with cling film and set aside for 10 minutes to allow the couscous to absorb the liquid. Drag a fork through the couscous to separate the grains.

Step 6

Stir the yellow peppers and sweetcorn into the couscous and mix well, then stir in the chilli and coriander (if using). Stir once more, then cover and place in the fridge until you are ready to serve.

Step 7

For the raita, coarsely grate the cucumber onto a clean tea towel, then gather the tea towel up and hold it over the sink. Twist it until all the liquid comes out of the cucumber. Tip the squeezed cucumber into a separate bowl, then add the yoghurt. Finely grate the garlic over the top and season with the ground coriander, a little salt and some black pepper. Stir well, then cover and place in the fridge until needed.

Step 8

Remove the foil from the lamb and baste with any juices at the bottom of the tray. Return to the oven for 15 minutes, until just browned around the edges.

Step 9

To serve, lay the pitta breads on a baking tray and cover with foil. Heat through in the oven for 5 minutes while carving the lamb. Remove the lamb from the tray and pull the meat from the bone, shredding the lamb into small pieces. Mix the shredded lamb back into the cooking juices and onion, stirring until combined.

Step 10

Divide the couscous between serving plates, top with shredded lamb and cooking juices, then serve a warmed pitta bread and a dollop of the raita alongside each portion. Serve immediately. Tip the remaining lamb (four portions) into an airtight container and leave to cool, then transfer to the fridge. The leftovers can be eaten cold or reheated in a microwave oven (see Tips).