Toss the steak strips in the cornstarch and some salt and pepper and set aside for 5 minutes. Heat half the oil in a wok or frying pan over a high heat and fry the steak until browned all over. Remove and set aside.
Heat the rest of the oil and fry the garlic, ginger and spring onions over a medium heat for 2 minutes.
Add the stir-fry vegetables to the pan with a splash of water and fry for 1 minute before adding the chile flakes, soy sauce and sugar along with 200 milliliters (3/4 cup) water. Return the steak to the pan with the noodles and bubble until you have a glossy sauce that coats the noodles. Serve straight away.