Steam the brussels sprouts for 8 minutes. Once they are cool enough to handle, thinly slice them about 1/8 inch thick. (If you have a new food processor, you can use the slicing disk if yours came with one! Saves a LOT of time.) Heat the oil in a large frying pan over high heat. Add the brussels sprouts and a pinch of salt and cook, stirring now and then, until their edges have started to brown. Remove the sprouts to a serving bowl, and squeeze the half lemon over them and add the sriracha and fish sauce. Stir well to coat and serve immediately!