Rub the lamb with olive oil and sprinkle very liberally with salt and pepper. Sear the lamb in a heavy bottomed skillet. Transfer to a casserole dish.
Add a little olive oil to the skillet, then add the onions. Cook until tender, then stir in the garlic and tomato paste and cook until they start to become incorporated with the onions. Add the diced tomatoes and broth and bring to a boil; season to taste with salt and pepper. Add the liquid to the lamb casserole. Cover it and bake until the lamb is very tender, about 2 hours 30 minutes.
Add the orzo and stir. Add some hot water if it starts to look dry and continue to bake, uncovered, until the orzo is cooked, 20 to 30 minutes.
Serve pieces of the lamb alongside the orzo and top generously with your choice of cheese.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.