Heat a chargrill or barbecue grill on medium-high. Add the beef and cook for 3-4 minutes each side for medium-rare or until cooked to your liking. Transfer to a plate and set aside for 15 minutes to cool. Cut across the grain into thin strips. Set aside.
Meanwhile, to make the dressing, combine the lime juice, fish sauce, soy sauce, garlic, chilli and sugar in a small bowl and mix well.
Place the beef, lettuce, capsicum, bean sprouts, green shallots, coriander and mint in a large bowl. Pour over dressing and toss gently to combine. Serve immediately.