Chop lemongrass, red onion, kaffir lime leaves and clean pak choi, broccoli florets and gai larn. Grind the lemongrass, onion and kaffir lime leaves in a blender to a coarse paste.
Heat the oil in a large pan or in a wok over medium heat and fry the lemongrass paste in it for 30 seconds until it smells fine. Add the vegetables, season with salt and stir well so that the vegetables are coated in the paste. Cover and shear for 3 minutes until it is soft.