Remove the lamb from the refrigerator and remove the netting and let it sit out at room temperature for 30 minutes
While the lamb is coming to room temperature, preheat the oven to 350° and make the spice rub and the stuffing as shown below
For the spice rub: If you are making your own spice rub, blend together in a bowl the cocoa powder, ground coffee, ginger, ancho spice and chipotle spice. Skip this step if you are using a pre-made mole rub.
For the stuffing: zest 2 oranges into a small bowl and stir in 1/3 cup white sesame seeds and 1/4 cup grated Mexican chocolate
Slice 3 onions, cut the zested oranges into wedges and place both ingredients into a large roasting pan. Sprinkle with 1 Tbsp of the spice rub blend. Drizzle with olive oil and mix everything together thoroughly with your hands. Set aside.
Open the lamb onto a cutting board and sprinkle the inside generously with salt. Sprinkle the mole spice rub on top of the salt (save a little to rub on the outside). Add the stuffing mixture to the inside of the roast (on top of the spice rub). Now, starting at the short end of the lamb leg, roll the lamb up tightly and secure with twine. (See video or instructions in the post for how to secure (or truss) the lamb with twine
Place the rolled lamb on top of the onion/orange/spice mixture in the roasting pan and place in oven. Roast for 1 hour rotating the pan halfway through. If it starts to dry out, add 1/2 cup water and baste every 20 minutes if desired. Insert a meat thermometer into the thickest part of the roast, and when it registers 125°F, roast about 30 minutes longer. See temperature and timing per pound charts in the above post.
Let the lamb rest at room temperature for 30 minutes before untying and carving it into thin slices. Serve with the onions and pan juices.