Pulse ¼ cup of onion, garlic, oregano, and parsley in a food processor, adding oil in a drizzle and scraping down sides as necessary until the mixture is pasty, or use a mortar and pestle to grind the spices.
Place the mixture in a small bowl, stir in the cumin, chili pepper, smoked paprika, and Sazon Goya, and set aside.
Remove the pork roast from the packaging and gently rinse it under cold water. Dry with a paper towel, and rub with salt and pepper according to preference (½-¾ teaspoon per pound is a reasonable estimate). Score the fat covering if desired.
Thoroughly rub the roast with the seasoning mixture, getting into as many of the crevices as you can. Marinate the roast in the fridge for 4 hours or up to 2 days before roasting.
When ready to roast, preheat the oven to 275℉ (135℃) while the roast comes to room temperature for about 30 minutes.
Line a roasting pan with foil, then layer the sliced onion and orange on the bottom of the pan. Pour in about ½ cup of orange juice, ½ cup of stock or water, and the spoon any leftover marinade. You might have to add some more liquid as it cooks if you want more sauce to serve on the side.
Place pork skin side up in the pan. Remove any seasonings stuck to the top of the pork skin.
Roast it for about 3 hours, uncovered.
Increase the oven temperature to 500℉ (260℃) and roast for another 15-20 minutes until the skin is crisp and puffy, rotating the pan every 5 minutes for even crispness.
The internal temperature should be 180-185℉ (80-85℃) on an instant-read thermometer.
Let the meat rest for 10-15 minutes before slicing; the meat should be tender. Serve with lime wedges and sauce from the marinade.
If you want super crispy skin, place the pork roast on top of a rack in a pan.