Heat 1 tablespoon of oil in wok over high heat; add in onion and stir-fry for 2 minutes or until browned; remove onion to a bowl.
For the sauce; in a saucepan over medium-low heat; add in ginger, garlic red pepper flakes and soy sauce, water and black pepper.
Add in the brown sugar to the saucepan then increase the heat to medium and boil 2-3 minutes or until thickened; remove from heat.
Toss the beef strips with the cornstarch to coat; let sit for about 8-10 minutes.
Meanwhile heat 1 cup oil in the wok until hot but not smoking; add in the beef and saute for about 2 minutes or until the beef is just cooked through (you do not have to cook the beef completely as it will cook more after) remove with a slotted spoon to a paper towel remove the oil from the wok.
Return the wok back to the heat and put the meat back in the wok along with the onions; then add in the sauce and cook for 1 minute stirring.
Cook for about 1 minute more.
Serve on rice and sprinkle a small amount of chopped onions over the top.