Crush the garlic and one teaspoon of salt in a pestle and mortar. Add the lemon rind, paprika, cumin, herbs and a good grinding of black pepper and crush to a smooth pulp. Stir in four tablespoons of the olive oil. Using a sharp knife, create lots of holes all over the lamb, and then rub in the paste, pushing it deep into the holes. Transfer the lamb to a large food bag and pour in the lemon juice. Place in the fridge to marinate overnight.
The next day, take the lamb out of the fridge about one hour before you want to cook it. Preheat the oven to 160C (325F), Gas Mark 3.
Lay two long pieces of parchment paper on top of two long pieces of foil – one widthways, the other lengthways to form a cross. Cut the potatoes into 2cm (¾ inch) slices, bring up the sides of the foil and pile the potatoes in the middle, drizzle with olive oil, then pour over the marinade from the lamb and tuck in the bay leaves, a sprig of thyme and one of rosemary. Sit the marinated lamb on top of the potatoes season with salt and pepper and scrunch the foil together tightly to enclose the lamb completely. Carefully lift into a roasting tin and roast for 2 hours until the lamb is meltingly tender.
Remove the lamb from the oven and increase the temperature to 220C (450F), Gas mark 7. Unwrap the parcel and scrunch the tin foil and parchment paper under the rim of the tin, then baste the lamb with the juices and return to the oven for another 20 minutes until browned.
Remove the lamb from the tin and wrap in the foil and set aside to rest.
Turn the potatoes over and return to the oven for another 30 minutes, then season with salt. While the potatoes are cooking, mix together the ingredients for the mint yoghurt in a bowl and season with salt and pepper. Combine the red wine vinegar, olive oil and some seasoning to make a dressing for the salad. Toss together the remaining salad ingredients, adding the dressing at the last minute just before you are ready to eat.
Shred the lamb from the bone and arrange on warmed plates with the roasted potatoes and some dressed salad. Add a spoonful of the mint yoghurt to each one to serve.