Slice the flank steak against the grain into 1/8" thick, bite-size slices. Dip the steak pieces into the flour to apply a very thin dusting to both sides of each piece of beef. Let the beef sit for about 10 minutes so that the flour sticks.

Make the sauce by heating 2 tsp of vegetable oil in a medium saucepan over med/low heat. Add ginger and garlic to the pan and quickly add the soy sauce and water before the garlic scorches. 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.

Heat up one cup of oil in a wok over medium heat until it's nice and 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. Used a large slotted spoon to take the meat out and onto paper towels, then pour the oil out of the wok.

Put the wok over the heat, dump the meat back into it and simmer for one minute. Add the sauce, cook for one minute, then remove the beef and onions with tongs or a slotted spoon to a serving plate.

Serve with brown rice.