Bash the medallions to approximately 3mm thin slices with a meat hammer. Mix all of the marinade ingredients together except for the spring onion. Mix the beef into the marinade. Leave to marinade between 30 minutes & 6 hours refrigerated. Heat a heavy based frying pan over a high heat then place the beef straight into the smoking hot pan. Sear for 30 seconds each side. Place onto a serving plate & scatter the sliced spring onions over. Serve with fresh coriander, kimchi & steamed rice.