Step 1: The lamb
Preheat the oven to 180C, which is 350F or Gas mark 4. Unwrap the lamb and slash the meat 20-30 times with a sharp knife. Poke small sprigs of rosemary into the lamb, place in a roasting tin and dribble with a tablespoon of olive oil. Season with salt and pepper and cover loosely with foil. In total, you're going to roast the lamb for just over two hours - but to start with, put it in the preheated oven and roast for an hour and a half. When you get to this point, you're ready to add the vegetables.
Step 2: The vegetables
While the lamb's roasting, cut a small aubergine and two peppers into chunks. Slice 3 courgettes, keeping the slices quite thick, and chop a red onion into wedges. Toss all the vegetables with 3 tablespoons of olive oil. When the lamb's been roasting for an hour and a half, take it out of the oven and remove the foil. Scatter the vegetables around the lamb and turn the oven temperature up to 220C/425F/Gas 7. Roast for a further 35-45 minutes, or until the lamb is cooked and the vegetables are tender and lightly charred. Turn the vegetables once during cooking to make sure they brown evenly.
Step 3: The gravy
Place the lamb and the vegetables on a serving plate. Cover it loosely with foil and leave it to rest. Spoon off as much fat as possible from the roasting tin. Place the tin on the hob and add 150ml of lamb stock. Bring the stock to the boil, stirring with a spoon to scrape up the pan juices. Simmer for a couple of minutes and season to taste.
Step 4: Serving
To serve, whip up a creamy mash from some boiled potatoes mashed with butter and milk, and steam some green veg. Carve the lamb, dish it up with the roasted vegetables, and drizzle with the pan gravy.