Pat the cut of pork dry on both sides and generously season with salt and pepper.
Make a rub from one tablespoon of oil, the oregano, cumin and any other spices you like with pork. Rub all over the meat. Place this in your slow cooker, which I tend to call a crockpot.
Roughly chop the onion and jalapeño, removing the inside veins and seeds. Add this over the top of the meat. Mince the garlic cloves and toss this in as well. Now juice all three limes and add this to the slow cooker as well.
Cook on low for 10 hours.
Remove the meat from the slow cooker liquid, brushing off any large onion or jalapeño pieces as you do. Shred the meat with forks into small pieces, removing the bone if you used a bone-in cut.
In a large cast iron skillet or nonstick pan, heat a couple teaspoons of oil or lard over medium-high heat. Add the meat to the pan and sprinkle the brown sugar over the top.
Cook for a few minutes, so you get those crispy edges and then flip. Cook another few minutes to get more crispy pieces and remove to a plate.