In a clay pot, sauté the onion with a little olive oil until it softens. Add the lamb and cook with the onion until the meat changes color. Then add boiling water, the spices, black pepper, and ginger (do not add salt yet). Cover and simmer on very low heat until the lamb is tender. Add the potatoes and green peas, and continue cooking until the vegetables are done.

Finally, add the green olives and a couple of slices of preserved lemon (do not add too much lemon; two slices are enough to give a delicious flavor to the tagine). Let it cook for another 5 minutes, then it's ready to serve.