Place the onion and carrots into a slow cooker. Heat the oil in a large non-stick frying pan, then fry the beef in two batches until golden-brown, transferring to the slow cooker when ready. Scatter with the garlic, ginger and chilli. Stir the sugar, miso, soy, stock and sesame oil into the juices in the frying pan then bring to a simmer, stirring to dissolve the miso and sugar. Pour the hot liquid over the beef and vegetables, cover with the lid and cook on low for 7½ hours. Scatter with the spring onions, re-cover the slow cooker then cook for another 30 minutes until the onions are tender. Stir in the beansprouts, then drizzle with a little more sesame oil. Serve with steamed broccoli abd boiled rice.