Mix the spices and cloves of garlic together in a small bowl.
Using a small pairing knife, make several incisions in the pork roast. Using your finger, push the cloves of garlic and spice mixture into the incisions.
Mix cider vinegar into the remaining spices and form into a loose paste. Rub the mixture all over the roast and pour excess into the roasting pan.
Arrange onion rings in the bottom of the roasting pan and place roast on top, creating an impromptu roasting rack.
Roast at 300 degrees for 4 hours. Every 30 minutes or so add a cup of water to the pan to prevent the drippings and cider mixture from drying out.
Remove roast from oven when it is falling apart tongs tongs or a fork. Let cool slightly and break the roast up with your hands. Allow it to mix back into the roasting juices and onions in the roasting pan.