Heat 2 teaspoons of oil in a small pan over medium low. Add the ginger and garlic and saute just until fragrant (about 1 minute). Add the soy sauce, water and brown sugar and bring it to a boil.
Boil for 3-5 minutes until the sauce has slightly thickened but is still lose. Set asied
Toss the thinly sliced top sirloin in the cornstarch. Gently shake off any excess.
Heat a large pan or wok over medium high heat, Cook the beef in small batches for about 2 min.
Once all the beef has been cooked, combine it with the sauce and heat over medium until hot and bubbly. Heat for 5 minutes.
Remove from heat and stir in green onions.
Serve over rice. Garnish with green onions and sesame seeds if desired.
