1) Rinse the pork roast and pat it dry with paper towels. Combine the red pepper, salt, and black pepper. Rub the mixture into all sides of the pork. Cover loosely with wax paper and refrigerate overnight.
2) Place the seasoned pork in a shallow roasting pan and let stand at room temperature 1 hour.
3) Preheat the oven to 300oF. Pour the vinegar to taste over the pork (more for a sharper flavor, less for a more mellow flavor). Scatter the chopped onions and green peppers into the pan. Roast the meat until a thermometer inserted into the thickest part of the roast registers 180oF. Spoon the pan juices over the pork a few times during roasting. Remove the roast and let stand 1 hour. Keep the pan juices.
4) Remove the meat from the bone, if necessary, and chop it into roughly 1 cm pieces. Heat the barbecue sauce in a large saucepan over a low heat until hot. Skim the fat from the pan drippings and add the drippings to the barbecue sauce. Stir the pork, onions and green peppers into the sauce and warm without boiling until heated through. Serve hot.