Put the spring onions and onion in a large bowl of iced water and soak for at least 5 mins (or up to 2 hrs) in the fridge, until the spring onions curl up.
When ready to serve, drain well, spin in a salad spinner or pat dry, then transfer to a medium bowl. Add the sesame oil, gochugaru and a pinch of salt, then toss to coat. Serve immediately.
GochugaruChilli powder or flakes made from Korean chillies, which have their own unique flavour. This condiment will become your chilli of choice to sprinkle on anything that needssome heat.