In a sauce pan, whisk together soy sauce, brown sugar, garlic, ginger, 2 teaspoons vegetable oil along with 1/2 cup water. Cook over medium heat until slightly thickened, about 5-10 minutes; set aside.

In a large bowl, combine flank steak and cornstarch.

Heat the 1 cup vegetable oil in a large saucepan or wok. Add beef and fry until browned and cooked through, about 1-2 minutes. Transfer to a paper towel-lined plate; discard excess oil.

Add beef to the prepared sauce mixture in the saucepan and cook over medium heat and cook until sauce thickens, about 2-3 minutes.

Serve over cooked rice and garnish with green onion. Serves 4-5.