Heat oven to 160C. Mix one tablespoon tomato paste,garlic,one tablespoon olive oil,sea salt and pepper and rub over the lamb. Place in a lightly oiled roasting pan with two cups water,cover the pan tightly with foil,and bake for three hours.
Heat remaining olive oil and gently fry onions for 15 minutes until softened. Add remaining tomato paste,tomatoes,cinnamon sticks,cinnamon,cumin,allspice,sea salt and pepper,stirring,then add orzo,mixing well.
Drain off most of the lamb juices from roasting pan and arrange orzo mixture around meat. Increase heat to 200C. Add hot stock or water and bake for 10 minutes or until orzo is tender and has absorbed most of the liquid.
Remove lamb,thickly slice,and serve with orzo. Scatter with coriander and serve.
Correction: The cooking time for this recipe has changed. The lamb cooks for three hours,not five hours as previously indicated.