Place the pork in a large bowl. In a small bowl, mix the sugar and salt; sprinkle all over the pork. Cover; chill at least 6 hours or overnight.
Preheat the oven to 300 degrees . Pat the pork dry. Transfer to a large roasting pan and roast, basting with pan juices every hour, until very tender, about 6 hours.
In a small bowl, mix the scallions, ginger, soy sauce, vegetable oil, lemon juice, sesame oil and 2 tbsp. water to make the dipping sauce.
Let the pork rest 15 minutes; transfer to a work surface and coarsely shred, discarding the fat. Serve with the dipping sauce, lettuce leaves, rice and sriracha.