Preheat the oven to 220°C, 425°F, gas mark 7. Score the lamb all over and season. Using a pestle and mortar, or in a food processor, pound or blend the mint leaves with the garlic and seasoning until smooth. Slowly add the olive oil and brush all over the lamb. Roast in the oven, brushing with the oil regularly until the lamb is cooked. Cooking times for the lamb: pink: 10 minutes for every 450g plus 20 minutes. Medium: 15 minutes for every 450g plus 20 minutes. Well done: 20 minutes for every 450g plus 20 minutes. Remove from the oven and allow to rest on a plate for 10 minutes. While the meat is resting, remove the fat from the roasting tin. Add the stock to the tin and make a light, tasty broth by boiling and dissolving all the goodness at the bottom. Cook the potatoes in a large pan of boiling, salted water for 5 minutes. Add the fennel and carrots and cook for a further 5 minutes. Then add the rest of the vegetables and simmer for another 5 minutes. Serve the vegetables in a shallow bowl with the lamb, sliced, on top and a little broth and mint oil drizzled over.