Place the pancetta in a food processor and pulse until it forms a paste. Add the garlic, lemon zest, orange zest, rosemary, parsley, brown sugar, chile flakes, capers and pinch of salt and thoroughly mix with the pancetta.
Put the pork belly skin side down on a cutting board; arrange the pork loin in the center. Roll the belly around the loin so the short ends of the belly meet. If any of the belly or loin overhangs, trim the meat. Unroll, then set the loin aside.
Pierce the skin side of the belly all over with a knife (or cross hatch score with a knife) so the fat will render during cooking.
Sprinkle both the belly and loin with salt and pepper on both sides. Score the flesh side of the pork belly with a knife, and then rub the pancetta paste into it. Add the pork loin back in the center then roll up and tie. Put it into a roasting pan with a rack.
Sprinkle the pork belly skin lightly with salt. Put in the oven and roast for 2 hours. Turn the heat up to 400 degrees F and bake until the skin is crisp and the internal temperature reaches 170 degrees F, another 1 1/2 hours.
Let the porchetta rest for 15 to 20 minutes, then slice and serve. Drizzle with olive oil and add some fresh black pepper on top if desired.