150g beef flank steak, thinly sliced
1 tablespoon vegetable oil
2 cloves garlic, minced
1 teaspoon ginger, minced
3 tablespoons soy sauce
1 tablespoon brown sugar
1/4 cup water
3 scallions, cut into 2-inch pieces
1/2 teaspoon cornstarch mixed with 1 tablespoon water
Cooked rice, to serve