Heat the oil in a frying pan and cook the onion for 5 mins over a medium heat until soft. Turn up the heat and add the steak to the pan. Stir-fry with the onion for 2 mins. Mix together the teriyaki sauce, ginger and garlic, and stir into the meat with 1 tbsp water. Cook for 1-2 mins more, then remove from the heat.
Cook rice following pack instructions, then divide between 2 bowls. Spoon over the meat, onions and any sauce, then top with the spring onions. Serve with some pickled ginger, if you like.