To make the sesame-onion noodles:
Thinly slice the white parts of the spring onions into rings. Trim the green ends and thinly slice lengthways into shreds (set aside to garnish the beef ).
Gently heat the sunflower or peanut oil, then stir in the sliced white onion and cook until fragrant. Pour boiling water over the noodles, drain and add the noodles and bok choy to the pan. Coat evenly and allow to warm.
Mix in the soya sauce and sesame oil, sprinkle with toasted sesame seeds and season to taste.
For the Asian-style seared beef: Remove the edge of fat from the meat before moistening it with the sunflower or peanut oil. Sear on a hot griddle pan, then allow to cool.
Slice the steak, then bash it between sheets of baking paper. Arrange the flattened slices on individual plates or a platter. Moisten with sesame oil and soya sauce before adding a grinding of black pepper.
To serve: Garnish the steak with the reserved shredded green onion and serve with the warm sesame-onion noodles.
Leftovers? Make a substantial salad by adding more bok choy leaves and moistening with sunflower oil and fresh lime juice.