Step 1: Heat oven to 300 degrees. Score meat's skin with a sharp knife, making a cross-hatch pattern.
Step 2: Pulse garlic, onion, oregano, cumin, chili, salt and pepper together in a food processor, adding oil in a drizzle and scraping down sides as necessary, until mixture is pasty.Blend in the vinegar.
Step 3: Rub this mixture well into pork, getting it into every nook and cranny. Put pork in a roasting pan and film bottom with water. Roast pork for several hours , turning every hour or so and adding more water as necessary, until meat is very tender.
Step 4: Finish roasting with the skin side up until crisp, raising heat at end of cooking if necessary.
Step 5: Let meat rest for 10 to 15 minutes before cutting it up; meat should be so tender that cutting it into uniform slices is almost impossible; rather, whack it up into chunks. Serve with lime.