Cut the salmon into 2cm cubes and toss with the cornflour. Set aside for about 5 minutes.
Heat a wok over high heat and add 1 tbsp of the vegetable oil. Add the garlic and spring onions and fry for about a minute.
Then add the carrots,beans and soaked shiitake mushrooms and stir fry for about 3 minutes until the carrots and beans are softened. You can add a little of the shiitake soaking liquid if the wok looks a little dry. Remove the vegetables from the wok and return the wok to the heat.
Heat the remaining oil in the wok and fry the salmon pieces for about 3 minutes until browned on all sides.
Add the sake,mirin,soy sauce and hoisin sauce and toss to coat the salmon. Return the vegetables to the wok and toss through.
To serve,fill the lettuce cups with the salmon mixture,scatter with sesame seeds and squeeze over a little lemon.