Preheat the oven to 190°C / 375°F / Gas mark 5.
Have to hand, a baking dish for the lamb.
Line a baking tray with greaseproof paper and set aside.
Remove the lamb from the refrigerator for half an hour before cooking.
In the baking tray, add the potatoes and carrots in and mix with roughly 1-2 tablespoons of olive oil and season with salt and pepper.
Cut the cloves of garlic into quarters, then with a knife make slits into the lamb, pressing the garlic into those slits.
Place the lamb into the baking dish and sprinkle the fresh rosemary and oregano on the meat. Turn the meat over and cover the underside with the herbs too.
Cut the lemons in half and squeeze the juice directly onto the lamb.
Pour enough olive oil over the lamb to coat it.
Season with salt and pepper.
Using your hands, massage the lamb thoroughly with the herbs, lemon juice, salt, pepper and oil until it is all completely coated.
Add a small cup of water to the baking dish then place, uncovered, in the oven and roast for 1¼ hours.
Place the baking tray into the oven and cook the vegetables until gently browned and you can pierce the potatoes easily with a fork or sharp knife.
The lamb will be cooked to medium at the 1 ¼ hour point.
Remove from the oven, wrap loosely in foil and allow to rest for 15 minutes before carving.