1 pound beef top sirloin steak
¼ cup soy sauce
2 tablespoons white sugar
2 tablespoons cornstarch
½ teaspoon ground ginger
3 tablespoons vegetable oil, divided
1 red onion, cut into 1-inch squares
1 green bell pepper, cut into 1-inch squares
2 tomatoes, cut into wedges
Slice steak into 1/2-inch thick slices across the grain.
Whisk together soy sauce, sugar, cornstarch, and ginger in a bowl until the sugar has dissolved and the mixture is smooth. Place steak slices into the marinade, and stir until well-coated.