Heat the oil in a stove top suitable casserole dish over a medium heat. Cook the lamb in batches until lightly browned. Remove the lamb and set aside. Cook the onion and garlic in the casserole dish until the onion is tender.
Return the lamb to the casserole dish. Add the coriander, cumin, paprika, salt and pepper while stirring to coat the lamb. Add the tomato paste and 1 cup of the water and bring to the boil. Cover and transfer the casserole dish to the oven. Bake for about 30 minutes.
Add the potatoes and remaining water. Cover and bake for 30 minutes or until the lamb and potatoes are tender.