Preheat the oven to 160°C regular bake.

Put the onions in a roasting dish that will hold the lamb snugly and season with salt and pepper.

Pat the lamb dry with kitchen towels. Using a sharp knife, score the lamb on both sides by making shallow cuts across the meat, deep enough to break through the skin. This allows the paste to penetrate and flavour the meat.

Combine all the remaining ingredients in a bowl. Rub a third of the paste over the bottom of the lamb, pushing it into all the cuts. Turn the lamb over, place on top of the onions and spoon over the remaining paste, making sure every bit of lamb is covered.

Cover with a piece of baking paper then seal tightly with foil (extra wide foil is good for this).

Roast for 5 hours. Remove the foil and spoon over some of the cooking juices then roast uncovered for a further 1 hour. Take the lamb out of the oven and loosely cover with foil and a tea towel on top, and rest for 15 minutes.

TO SERVE: Crumble half of the feta over the lamb then spoon over half of the gremolata, serving the rest separately. Serve with the onions and spoon over some of the pan juices.

Herb and Caper Gremolata 

⅓ cup finely chopped red onion 
2 tablespoons lemon juice
1 packed cup parsley, finely chopped
½ packed cup mint leaves, finely chopped
3 tablespoons extra virgin olive oil
2 tablespoons capers
2 teaspoons finely grated lemon zest 
½ teaspoon chilli flakes sea salt and ground pepper

Combine the onion and lemon juice in a bowl and leave for 10 minutes. Stir in all the remaining ingredients and season well with salt and pepper.