Preheat the oven to 425°F.
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 to your mixture then brush all over the lamb. Roast in the oven for 1½ hours, brushing with the seasoned oil regularly until the lamb is cooked.
While the meat is resting, remove the fat from the roasting pan. Add the stock to the pan 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.
Carve your lamb, then serve the vegetables in a shallow bowl with the lamb on top and a little broth and mint oil drizzled over.