Place all the salad dressing ingredients into a food processor/blender and pulse together until well combined. Adjust the seasoning to taste and refrigerate until ready to serve.
Lightly coat the skirt steak in sesame seed oil and rub with the five-spice powder.
Grill the steak on a hot fire or griddle pan, turning to cook for 5 to 6 minutes on each side for medium rare or to your preferred doneness.
Remove the steak from the pan, transfer to a chopping board and allow to rest for half its cooking time before slicing.
Spoon the tangy Vietnamese dressing over the five-spice skirt steak and serve with steamed pak choy and Jasmine rice. Garnish with sesame seeds and fresh chilli.