Trim all fat and silver skin from meat. Lay steaks out horizontally on the cutting board with the grain running vertically. Slice the slab into manageable sized pieces. Then cut the meat opposite the grain (horizontal) into bite-sized pieces.
Dust steak pieces lightly in cornstarch and set aside while preparing the sauce.
In a small sauce pan heat oil over medium high heat. Add ginger and garlic. Add soy sauce and water to the ginger and garlic before it browns. Add brown sugar and whisk until dissolved. Bring sauce to a boil and simmer about 10 minutes or until slightly reduced and thickened. Remove from the heat and reserve.
In a large skillet or wok heat 1/3 cup oil over medium high heat. Working in batches, add the steak a few at a time to the hot oil. Cook about 1 minute without touching the meat then flip each piece and cook 1 minute more. Remove meat while still rare inside, and continue with next batch. Once all meat is browned, pour off oil and wipe out skillet.
Heat skillet over high heat and add mushrooms. Cook a couple of minutes or until mushrooms are slightly softened and browned. Reserve in separate bowl.
Add steak to the hot pan and cook about 1 minute. Add sauce to the pan and simmer and toss meat and sauce about 1 minute. Add mushrooms and green onions. Toss with steak and sauce and heat 1 minute. Serve over rice.
by The Savvy Kitchen