Place garlic, salt, peppercorns and oregano in the bowl of a food processor. Process until garlic is chopped. Add olive oil and vinegar and process to form a thick paste. Place pork in a large roasting pan fat side up and score top with a sharp knife. Rub garlic mixture over meat; refrigerate at least 3 hours (I prefer overnight).
Preheat oven to 350.
Place pork in oven and roast about 3 hours, until the internal temperature reaches 160. Let pork cool slightly and then chop or tear into large chunks.