Heat oil in a large frying pan. When the pan is
really hot, tip in the beef and pepper, then cook
for a few mins until lightly browned and the
beef is cooked through. Tip in the garlic, ginger
and sesame seeds, then cook for 1-2 mins more,
stirring often until they start to turn golden.
Pour over the soy sauce and 2 tbsp water, let
it bubble down a bit until it starts to look syrupy,
then drizzle with the sesame oil. Separate the
leaves from the lettuces and arrange on a plate.
Spoon a little of the beef mixture into each leaf,
drizzle with pan juices and serve warm.