Preheat the oven to 180°C.
Mix the flour and dried rosemary with a pinch of salt and pepper. Coat the lamb in mixture. Heat oil in a non-stick frypan over high heat and fry the lamb in batches for 2 minutes each side until browned.
In a large bowl, combine the onion and tomato, then season with salt and pepper. Lay 6 of the lamb pieces in the bottom of a large, deep baking dish and top with half the tomato mixture. Sprinkle over 1 tablespoon of sugar and half the fresh rosemary. Repeat for the second layer.
Cover with foil and bake for 3-4 hours or until the meat falls off the bone. When you are ready to serve, blanch the peas in boiling water for 1 minute, drain, then stir them through the lamb. Serve on a bed of mashed potato.