Rinse the meat and pat dry with kitchen paper. Cut into large pieces and put in a bowl with the vinegar. Refrigerate for 2 hours.
Remove the meat from the vinegar and pat dry with kitchen paper.
Place the lamb pieces in a shallow saucepan. Sprinkle the oregano and a pinch of sea salt on top. Scatter the circles and over the meat and pour in the olive oil.
Cover the saucepan with a lid and cook over a very low heat for 1 hour 30 minutes. If the pan juices start to dry up, add a little boiling water.
Notes from the cook
Buy the lamb shoulder in one piece and dice it yourself in large enough pieces to ensure the meat stays succulent throughout the cooking process. Small pieces tend to shrink to a stringy mess.
If you're a meat-eater you won't believe how good this vegetarian dish tastes!