Heat oil in the dutch oven, or kettle, on a very high flame and add the onions. Cook the onions, stirring occasionally for 5-7 minutes, and add the lamb.
Cook the lamb for 10 minutes and add the carrots. Keep cooking for 10 more minutes.
Add cumin, coriander, salt, pepper and 4 cups of water. Bring to a boil.
Peel some of the skin off the garlic head and slice the top off, exposing the garlic cloves, and then add it to the meat. Reduce heat to medium-low, cover with lid and cook for about 1 hour. Meanwhile, wash the rice thoroughly.
Taste the liquid for salt and adjust if necessary. Add the rice and spread it out evenly.
Add 3 cups of boiling water, reduce heat to low, cover the dutch oven with lid and cook for 25-30 minutes. At the end of cooking time, check if the water has been absorbed fully, and, if not, let it cook a little longer. Once ready, let it rest for 15 minutes before serving.