Add the bunches of washed spinach, press down, and squeeze a lid on top. You may have to add the spinach in stages, as it wilts and makes room for more.
Once the spinach has wilted enough, add water to reach just below the top of the meat, cover with a lid, bring to a simmer, and then turn the heat down and cook gently for about one and a half to two hours, until the lamb is falling from the bones. Take the lid off if you'd like to reduce to the juices more.
Taste and check seasoning.
Serve as is, with spoons for the juice, or over a bed of rice.