Cut slits in lamb; insert garlic. Rub meat with salt, pepper and oregano. Roast at 400° for 30 minutes. Reduce heat to 350°; roast 1 hour more Stept 2
Skim off any fat in pan; pour tomato sauce, water and lemon juice over lamb. Place artichokes and, if desired, lemons around meat. Roast 1 hour longer or until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°). Let stand for 15 minutes before slicing. If desired, garnish with fresh herbs.