Heat a medium skillet over medium-low heat. Place the bacon in the pan and cook until some of the fat is rendered but the bacon has not browned. Drain bacon on paper towels.
Rub the lamb with salt and pepper, garlic, and oregano. Allow lamb to reach room temperature and let stand for 1 hour. Preheat oven to 350°F.
Place lamb in a heavy roasting pan. Arrange bacon over top of lamb in a crisscross pattern. Top with the onion slices. Cook 15 minutes.
Remove lamb from oven, and spread the currant jelly on top of the bacon and onions.
Return to oven and baste every 20 minutes with the pan drippings. Continue cooking until an instant-read thermometer inserted in the thickest part reads 135°F, about 2 hours. If the pan juices evaporate, add some water to the roasting pan. Transfer the lamb to a platter. Serve with pan juices and currant jelly.
For pan sauce: Use the pan drippings as a "pan gravy" by adding a bit of flour (and perhaps a little water) to make a thicker gravy for your gravy boat.