Preheat a grill to medium.
Rub the pork loin well on all sides with the olive oil, and season it with the kosher salt, cumin, and black pepper. Place the pork loin, fat side down, onto the grill and cook for 5 minutes. Rotate the pork 90 degrees and cook for another 5 minutes. Then turn the pork over and cook for a final 5 minutes. Remove the pork from the grill and place it in a small grill-proof roasting pan that holds it snugly.
In a medium bowl, combine the orange juice, lime juice, vinegar, and marmalade, and whisk well to combine. Drizzle the citrus mixture over the pork. Place the roasting pan directly on the grill, close the lid of the grill, and cook for 5 minutes. Raise the lid and baste the pork with the pan juices. Close the lid and cook for an additional 15 to 20 minutes, basting every 5 minutes, until the pork reaches an internal temperature of 140 degrees. (Take care not to overcook it.)
Remove the pork from the grill. Add the cilantro to the roasting pan, and swirl it in the pan juices. Allow the pork to rest for 7 to 10 minutes before slicing. Serve the pork thinly sliced, drizzled with pan juices.
Yield: 6-8 Servings