In a medium bowl add the first 5 ingredients for the sauce in a medium saucepan. Cook on medium until a bit thickened for 10 minutes. Set aside.
In a large Ziploc bag combine the cornstarch and flank steak.
Add 2 tsp of oil to a medium saucepan. Cook on medium low. Add ginger and minced garlic. Cook until fragrant about 2 minutes. Set to side.
Add half of the oil in a large sauce pan and half of the steak and fry until brown about 2 minutes. Place steak on a paper towel. Set to side.
Do the same step above for the rest of the steak.
Add the beef back to the pan and then add the sauce, ginger and minced garlic.
Cook on medium heat until sauce thickens, about 4 minutes.
Add green onions on top and serve immediately over rice.