Combine all the ingredients from the green onions through to the butter (everything but the dried lemon and the lamb) in a food processor or blender, and process until well blended and has turned into a thick paste consistency. If you need to, add a splash of water if the sauce is so thick it won't combine well.
Pour this green sauce over the lamb shanks and toss to coat thoroughly, then cover tightly by placing a sheet of parchment paper on top of the lamb, then sealing with foil and marinade for as much time as you have- anywhere from 4 hours to overnight.
When it's time to cook the lamb, preheat the oven to 465 F (240C). Place the foil covered pan in the oven for 1 hour. After 1 hour, reduce the temperature to 350 F (180C) and cook for another 2 hours. Halfway through, toss the lamb, flipping the pieces over. When 30 minutes of cooking time remain, uncover the dish so that the outside of the lamb crisps up a little.
Serve with rice of choice, preferably topped with toasted nuts and garnished with chopped cilantro (coriander)