1. Mince garlic, then combine with sugar, soy sauce, salt and pepper. Rub over pork and let stand 1 hour. Meanwhile preheat the oven to 350 degrees.
2. Place pork on a rack over a roasting pan containing several inches of water, and roast 1 hour. Meanwhile cut lettuce in 1-inch sections.
3. Remove pork and drain off fat. (Set rack aside.) Line bottom of pan with lettuce; place pork on top. Return to oven and roast 45 minutes more.