Remove excess fat from lamb.
Combine garlic, pepper and oregano. Crush garlic, work spices into a paste. With the point of a sharp knife, make 3 - 1 inch slits several inches apart in lamb down to the bone.
Put 1/4 of seasoning mixture into slits, pressing down close to the bone. Rub lamb well with lemon juice and spread on remaining seasoning. With a spatula, cover lamb with 1/2-inch coating of plain yogurt; refrigerate overnight. Two hours before roasting set lamb out at room temperature.
Preheat oven to 350° F. Place lamb on a rack in a roasting pan and roast for 3 to 3 1/2 hours. Every half hour, baste with remaining yogurt marinade.
Servings: 10 to 12