Heat 1/4 cup oil in a large saucepan over medium-low heat. Add onion and cook, stirring, for 5 minutes or until softened. Increase heat to medium and add garlic and lamb. Cook, stirring frequently, for 5 minutes or until meat is browned on the outside. Pour in the 1 1/2 cups water and season with salt, pepper, cayenne pepper and cumin. Bring to a simmer. Reduce heat to low. Cover the pan and cook for 1 1/2 hours.
Meanwhile, heat the extra oil in a large saucepan over medium-high heat. Add rice and cook, stirring, for 5 minutes. Add extra water and bring to a boil. Reduce heat to low and cook, loosely covered, for about 30 minutes, or until rice is tender.
Add spinach and coriander to the meat mixture and cook for another 10 to 15 minutes. Mound the rice on a platter, and spoon some of the lamb stew over. Put remaining stew in a separate serving bowl.