Brush the steak
with the oil and heat a heavy-based frying pan or wok over high heat. Add
the steak to the pan and cook for about 4 minutes each side, turning the
steak once only. Remove from the pan and set aside for 5 minutes. To make
the dressing, combine the fish sauce, lime juice, soy sauce, sweet chili
sauce, garlic and coriander in a bowl. Cut the cooled steak into thin
strips. Place the lettuce leaves on a serving plate and arrange the cherry
tomatoes, cucumber, spring onion and strips of steak on top. Drizzle with
the dressing and scatter over the coriander leaves. Serve immediately.