Slice the flank steak against the grain (the grain is the length of the steak the long way into 1/4 inch think pieces and add it to a Ziploc bag with the cornstarch.

Press the steak around in the bag making sure each piece is fully coated with cornstarch and leave it to sit while you make the sauce.

Add the canola oil to a large frying pan and heat on medium high heat.

Add the steak, shaking off any excess corn starch to the pan in a single layer and cook on each side for 1 minute.

If you need to cook the steak in batches because your pan isn't big enough do that rather than crowding the pan, you want to get a good sear on the steak and if you crowd the pan your steak with steam instead of sear.

When the steak is done cooking remove it from the pan.

Add the ginger and garlic to the pan and sauté for 10-15 seconds.

Add the soy sauce, water and dark brown sugar to the pan and let it come to a boil.

Add the steak back in and let the sauce thicken for 20-30 seconds.

The cornstarch we used on the steak should thicken the sauce, if you find it isn't thickening enough add 1 tablespoon of cornstarch to 1 tablespoon of cold water and stir to dissolve the cornstarch and add it to the pan.

Add the green onions, stir to combine everything, and cook for a final 20-30 seconds.

Serve immediately.