Slice the sirloin steak across into thin slices. Add to a bowl and sprinkle over the cornflour and white pepper, then mix well.
Add the water, oyster sauce and sunflower oil to the bowl with the steak slices.
Mix the sauce ingredients together in a separate bowl and set aside.
Cook the noodles according to pack instructions.
Heat 100ml of oil in a pan and fry the noodles until crispy. Remove and keep warm.
Stir fry the beef over high heat until cooked through.
Add the vegetables and continue to stir fry for a couple of minutes.
Add the sauce and allow it to bubble and thicken.
Divide the noodles between serving bowls and pour the steak mixture over them.
Serve topped with a few more spring onions.