Heat the oil on high in a large pan or casserole dish.
Fry the lamb in two or three batches until brown on all sides.
With a slotted spoon, remove the lamb from the pan and place on a plate.
Lower the heat, add the butter to the pan and when it starts to foam add the onion and green pepper and sauté until soft but not browned. Add the garlic a couple of minutes before the end of the cooking time.
Mix the tomato purée with 2 tbsp of boiling water then add, stirring for a minute or two.
Return the lamb and its juices to the pan then pour in the chopped tomatoes, dried herbs and seasoning.
Fill the empty tomato can half full of water, swill out and add to pan – the meat should be just covered by liquid.
Bring to the boil then reduce the heat, cover with a lid and simmer gently (or you can put it into an oven preheated to 180˚C, gas mark 4). Cook for 1 hour. If cooking this dish in advance, it can be set aside at this stage.
Trim the green beans and lay them on top of the casserole.
Cook for a further 30-40 minutes until the meat and beans are tender.
Spinneys Nutritionist, Freda Molamphy, says: "Lamb is rich in high-quality protein and iron. Its fat content can vary depending on the cut and also on the animal's diet and feed. Lamb steaks tend to be leaner than other cuts."