Slice the flank steak against the grain into 1/4" thick bite-size slices. Dip the steak pieces into the marinade. Let the beef sit for about 30 minutes so that the cornstarch sticks.

Make the sauce by heating 2 tsp of vegetable oil in a saucepan over med/low heat.

Add ginger and garlic to the pan to fry, then add all the remaining sauce ingredients (minus the sugar).

Dissolve the brown sugar in the sauce, then raise the heat to about medium and boil the sauce for 2-3 minutes or until the sauce thickens.

Remove it from the heat and set aside.

Heat up one cup of oil in a wok until its hot but not smoking. Add the beef to the oil and saute for just two minutes, or until the beef just begins to darken on the edges. Stir the meat around a little so that it cooks evenly.

After a couple minutes, use a large slotted spoon to take the meat out and onto paper towels, then pour the oil leaving about 1 tsp of oil in the wok. Put the pan back over the heat.

Add the onions, then add the green onions. Cook for one minute.

Add the beef back in and add the sauce. Cook for one minute.

Serve on a bed of jasmine rice and garnish with coriander.