If using a griddle or frying pan, place over a high heat until very hot. Cook the steak over medium-hot coals on the barbecue or on the pan for 10–12 minutes until well marked on the outside and rare to medium-rare inside. Season with salt and set aside to rest for up to 2 hours.
Place the cucumber, shallots, cherry tomatoes, chilli, herbs and spring onions in a large bowl and gently toss together to combine. Cover with clingfilm and chill until needed.
To make the dressing, dissolve the sugar in a screw-topped jar with the lime juice. Add the ginger, chilli and sesame oil and shake until well combined. Set aside until needed.
To make the peanut sauce, place the peanuts in a blender with 3 tablespoons of water, the sunflower oil, soy sauce and chilli sauce. Blitz to a puree and season to taste.
To serve, thinly slice the beef – it should be nice and rare. Whisk any meat juices into the peanut sauce. Combine the cucumber mixture and salad leaves with the Asian dressing. Divide the salad between plates and pile the beef mixture high on top. Drizzle over the peanut sauce to serve.