Preheat oven to 200°C (180° fan-forced). In a small bowl place oil, 2 teaspoons wasabi, chives and mint. Season and stir to combine. Brush tops of lamb rumps with wasabi mixture.
Place lamb on a rack in a roasting tin. Cook in the oven for 20 to 25 minutes or until cooked to your liking. Set aside covered with foil to rest for 5 minutes. Thinly slice.
Meanwhile in a small bowl combine remaining wasabi and yoghurt. Season, adding a little water to thin if necessary.
To serve, place cucumber, carrot, pear, Asian leaves, and lamb into buns. Drizzle with yoghurt, top with ginger and serve with lime wedges, if desired.
