For the day you prep (or the morning of the day you want to cook it) we need to let the goodness get all soaked in the beef. Slice the flank steak to about ½ inch wide strips – or if it is precut, you can skip this step! Put all the meat into a gallon-size freezer bag. Mix the ginger powder, garlic powder, and cornstarch together and sprinkle over the meat. If you want to add the red pepper flakes for a lil spice, go for it now, personally I like to rub the pepper between my hands to release the natural oils. Squish the meat all around in the bag until you get all the meat covered with the powder. Once covered, add the soy sauce and again squish the meat around in the bag until all the meat is covered.