Finely chop the lemongrass and chilli, grate garlic and ginger. Place aromatics in a shallow dish with sugar, fish sauce, lime juice, and olive oil. Add steaks and turn to coat. Leave to marinate, and come to room temperature, for 30 mins.
When ready to cook, pre-heat barbecue or a heavy-based skillet to medium-high. Scrape excess marinade from steaks and season with salt. Cook for 3 mins each side, or until cooked to your liking. Transfer to a clean plate, cover with foil and rest 3 mins.
Whisk together extra lime juice, sugar, sesame oil and olive oil, season with salt and pepper. Toss dressing and chopped nuts though salad. Slice steak and serve with dressed salad and extra lime wedges.
To make a slaw at home, finely shred a quarter of a red cabbage and half a bunch of kale, combine with two grated carrots and one sliced spring onion.