Flank steak is mostly used for this dish, but I think any part can also be used as well. The steak is cooked as however you preferred (usually a medium rare) and the dressing can be mixed up with the basic ingredients that you can find at any Asian store and they can be substituted if you feel uncomfortable to use them, like use sea salt instead of fish sauce and omit the roasted rice powder. The dressing should have a balance of salty, sweet, and sour, however, there is no rule for that. I’d say, there are two essential ingredients for the dressing – the roasted rice powder and mint leaves. Though you can omit the rice powder since sometime it can be hard to find but never forget the mint leaves.