In a mortar and pestle, mash the garlic cloves, salt, peppercorns, onion, oregano, cumin, and olive oil until you get a paste. Set aside.
Place the pork shoulder in a roasting pan. Grab the thick pork skin and using a knife, gently separate the skin from the pork enough for it to flap over. Do not cut it off completely.
Pierce the pork a few times with the knife and pour the mojo marinade over it. Next, rub the garlic paste, evenly, over the pork and then place the skin back down. Cover the entire pork roast with aluminum foil and place in the fridge to marinate for 2-3 hours or overnight. The longer, the better.
Preheat oven to 375 degrees F. Remove the pork from the fridge, allow it to come to room temperature, and pat the skin down with a paper towel before roasting. The dryer the skin, the crispier it will be.
Lightly spray aluminum foil with non-stick cooking spray and cover the roasting pan. This will help the foil not get stuck to the skin while in the oven.
Place the pork shoulder in the oven and roast for 4 hours until the internal temp is 180 degrees F. (A good rule of thumb is to roast the pork for 30 minutes for every pound. An 8 pound pork roast would cook for 4 hours.)
Remove the roasting pan from the oven. Increase the oven temp to 450 degrees F. Remove the foil and drain the liquid but do not discard it. Bake for another 30 minutes, uncovered, to crisp up the skin. Keep an eye on it to make sure it doesn’t burn!
Remove from oven and allow to rest for 20 minutes before shredding with two forks. Feel free to pour leftover marinade mixture over the shredded pork. Serve and enjoy!