How to Make It
Set the pork on a work surface. Using a small, sharp knife, make 1-inch-long slashes in the skin, about 2 inches apart. Rub the garlic into the slashes and along the underside of the pork.
In a large glass or ceramic bowl, combine the vinegar with the lime, grapefruit and orange juices, oregano, pepper, adobo seasoning and Sazón. Stir in the green pepper and onion, then add the pork, skin side up. Refrigerate overnight, turning the meat once or twice. Bring to room temperature before cooking.
Preheat the oven to 400°. Transfer the pork and its marinade to a roasting pan. Cover with foil and roast for about 3 hours, or until the meat is very tender. Let cool in the liquid. Transfer the pork to a cutting board and discard the skin and fat. Strain the pan juices into a glass measure and skim off the fat. Slice or shred the meat before serving.