In a mortar and pestle, if you have one... combine the Oregano, Rosemary, Garlic and Cinnamon. Then add the Oil and Lime juice to make a paste.
Make small cuts into the lamb meat and push the paste into all the cuts and cover all the lamb with it. Put into an airtight container and leave in the fridge overnight. (smells awesome!)
Peel and slice the Sweet Potatoes into a large covered oven dish. Place the lamb portions on top, tipping over any remaining paste. Add the veg down the sides.
Create the stock with the cubes and boiling water, pour down the side of the meat, over the veg,trying to not wash off the marinade from the meat. Cover and cook in a very hot oven for 30 minutes, then reduce the heat to medium- low for 1 hour 30 minutes.
Check to see if the meat is cooked by stabbing with a knife, should go through easy. (If not, return for another 30 minutes, medium hot.) Serve and enjoy!
