In a medium bowl, mix together the lime juice, soy sauce, sugar, ginger, garlic, and salt until the sugar dissolves.
Place the loin of pork in a roasting pan, and scatter the onion rings and bay leaves over it. Pour lime-ginger mixture over the meat, and cover with plastic wrap. Refrigerate for 12 hours or so, turning every once in a while.
Preheat the oven to 325 degrees F (165 degrees C).
Roast, uncovered, for about 3 1/2 hours; baste frequently with pan juices. For a well done roast, cook until the internal temperature of the roast is 145 degrees F (63 degrees C).