Slice beef into thin strips and set aside.
In a bowl, mix together ginger, garlic, brown sugar, soy sauce, and sesame oil.
Add marinade to the beef and marinade in the fridge for at least 4 hours. Overnight is best.
Heat up your frying pan (a wok is best) until close to smoking. You won't need to add oil to the pan since there is oil in the marinade.
Add in your meat and marinade and cook until brown. This only takes a few minutes. Be careful not to overcook the meat or it will become chewy.
Remove from heat and serve over white rice. Top with green onions.