Place the steak in a bowl. Add the ginger, garlic, soy sauce and cornstarch and toss to coat. Marinate the beef 20 to 30 minutes. Heat 2 Tbsp. of the oil in a large skillet or wok over high heat. Add the beef and stir-fry until nicely coloured, about 2 to 3 minutes. Remove the meat from the pan. Add the remaining oil to the pan. Add the onion and broccoli and stir-fry 2 to 3 minutes. Add the remaining ingredients and bring to a boil. Return the beef to the pan and heat through. Spoon onto a platter and serve.