1.Pan-fry steak until seared on both sides and cooked to your liking. Transfer steak to a plate, cool slightly, then cover and refrigerate for at least 1 hour. Cut chilled steak into wafer-thin slices.
2.Place vermicelli in a heat-resistant bowl, cover with boiling water and stand for 5 minutes, stirring to separate strands. Drain vermicelli in a strainer, rinse under cold water, then drain again, pressing down firmly to remove excess liquid.
3.Immerse a rice paper wrapper briefly in a dish of warm water to soften. Place wrapper on a chopping board. Spread approximately 1 tsp sweet chilli sauce on one end of wrapper, then layer a little lettuce, vermicelli and sliced steak over sauce. Start rolling up from filled end, turning in sides. When wrapper is half rolled up, place 1-2 coriander leaves on top and continue rolling up to enclose filling and coriander leaves and form a neat roll. Repeat this process with remaining wrappers and filling ingredients.
4.Serve with extra sweet chilli sauce.
Rice paper wrappers are available from the Asian food section in supermarkets. Filling ingredients can be prepared several hours ahead. Keep covered in the refrigerator. Rolls can be prepared up to 2 hours ahead. Place on a tray lined with plastic wrap, then cover with a clean, damp tea towel and keep refrigerated.