Mix together the beef steak and the barbecue marinade and leave in the fridge for a minimum of 30 minutes.
Meanwhile, put the cabbage in a large bowl and sprinkle with salt. Set aside for 15 minutes, then rinse thoroughly in cold water. Drain and dry thoroughly. Add the carrots and spring onion. Combine the garlic, chilli sauce, sugar, fish sauce and rice wine vinegar and drizzle this over the vegetables. Transfer to an airtight container and set aside until required.
Heat ½ tbsp sesame oil in a large griddle pan over a high heat. Flash fry the beef strips until caramelised. Meanwhile, cook the noodles according to the instructions on the packet. Drain and dress with the remaining sesame oil and rice vinegar.
Toss the beef strips through the noodles, then divide this between the lettuce leaf cups. Top each with the salad and sprinkle with toasted sesame seeds.