In a small bowl, soak the currants in enough Port to cover for at least 2 hours and up to overnight. When ready to roast the lamb, drain the currants; discard the Port. Position a rack in the lower middle of the oven and heat the oven to 400°F.
In a large bowl, mix the bread-crumbs, mint, parsley, olive oil, pine nuts, and currants. Season to taste with salt and pepper. Add the beaten eggs and mix well.
Untie the lamb and unroll it. Lay the meat flat and pat dry with paper towels. Trim any excess fat and, if necessary, butterfly portions of the lamb to make it roughly rectangular and evenly thick. Sprinkle the inside of the lamb with salt and pepper and pat the stuffing evenly over the meat. Roll up the lamb tightly, from one short end to the other, and tie the roast snugly at 1-inch intervals with kitchen twine.
Sprinkle the outside of the lamb with more salt and pepper and then set it, seam side up, on a rack in a small roasting pan. Gather up any stuffing that escaped and poke it back in at the ends of the lamb roll. Roast until an instant-read thermometer inserted into a thick part of the roast reads 125° to 130°F (for medium rare), 60 to 70 min. Let rest for 15 min. and then carve into medium-thin slices. Serve topped with the red onion jam.