Step 1

Slice flank steak against the grain into 1/4-inch-thick pieces. Transfer beef slices to a large bowl.

Step 2

Marinate sliced beef with marinade ingredients as listed above and set aside to marinate for 15 minutes at room temperature. Do not marinate past 30 minutes or this over tenderizes the beef and changes the taste.

Step 3

In a small bowl, combine the sauce ingredients as listed above and set aside.

Step 4

Heat vegetable oil in a large pan on medium heat, fry beef until cooked through and slightly browned, about 4-5 minutes. Remove cooked beef from the pan and set aside.

Step 5

Sauté onions and mushrooms until slightly softened, about 2 minutes. Then pour in the sauce and simmer to thicken it.

Step 6

Toss in cooked beef and green onions until beef is evenly coated in sauce, about 30 seconds. Serve and enjoy!