Chop the garlic, rosemary, thyme, and oregano and combine with the zest of 2 lemons.
Season the lamb with salt and pepper. Place in a large ziplock bag, and add the herb and garlic mixture. Seal the bag and marinate overnight.
Bring the lamb to room temperature. Tie it with string so it forms a roast. Place it in a large roasting pan.
Peel the potatoes and quarter them. Toss them with some olive oil, salt and pepper and place them around the lamb. Squeeze the juice of 2 lemons over the meat and potatoes and drizzle with the olive oil.
Preheat the oven to 375 F/180 C
Roast the meat on the bottom rack of the oven uncovered for 1 to 1½ hours (***) till golden and crispy
Remove the lamb and tent with foil, and let rest 15-20 minutes before carving and serving. If the potatoes haven’t browned enough, return them to the oven. Increase temperature to 450 F/230 C and continue cooking while the meat is resting.
*** roast lamb approximately 25 minutes per pound for medium-rare. Internal temperature should register 145-155 F / 63-68 C when done.
145 F / 63 C for medium-rare
160 F /71 C for medium
170 F /77 C for well-done