Combine all ingredients except the lamb shoulder and oil in a mortar and pestle or a food processor. Grind/pulse the mixture to break it up, then add the oil, one tablespoon at a time, mashing to make a loose paste.

Pierce the lamb all over with a paring knife, rub with the marinade, then vacuum seal or put in a bag and allow to marinate overnight.

The next day, wrap the lamb shoulder in parchment paper and bake for 2 hours at hours at 250 F. Increase the heat to 275 F and bake for 2 more hours, or until the meat feels soft when you push on it through the paper. Most lamb or goat shoulders should be tender at the 4 hour mark, but if they aren't, turn the heat down to 250F and cook for another hour. Remove the lamb from the oven allow to rest for a few minutes before serving, then cut open the paper and carve.