Put all the marinade ingredients into a bowl and stir to combine. Add the beef and marinate for 15 minutes.
Heat a pan over a high heat and add the oil. Cook the steaks until browned on one side, then cook the other side. Add the marinade and cook for a few seconds. Put the steaks onto serving plates and keep warm. Add the mushrooms to the pan and cook until softened.
Place the mushrooms alongside the steak on the serving plates and garnish with orange segments and spring onions, if using. Serve with mixed salad leaves or steamed jasmine rice.