Slice the beef into 5mm thick strips, and set aside until needed.
Peel the ginger, and slice thinly cross-wise, then into matchsticks.
Remove the root end of the garlic cloves, smash and peel. Chop the garlic.
Remove the woody tail from the chillies, cut in half lengthwise. Scrape out the the spongy rib and seeds, if the chillies are too hot, and slice thinly.
Add the ginger, garlic, chillies, soy sauce, rice vinegar, sunflower oil and corn flour to the beef. Toss to coat evenly, and set aside until needed, up to 3 days in the refrigerator.
ROughly chop the coriander, stalks and all, and set aside.
Top and tail the peppers and onion, and slice into 5mm sticks.
Trim any dry ends from the spring onions, and cut into 2cm batons.
Heat a wok until begins to smoke. Add the beef to the wok and stri fry for about 2 minutes.
If you prefer the beef slightly on the rarer side, remove from the pan before proceeding with the next step.
Add the peppers, onion and spring onions to the pan, and cook for a further 3 minutes. If the juices in the pan have become too thick, add a splash of water to create some sauce. (Return the beef to the pan if it was taken out.)
Garnish with the chopped coriander, and serve immeditately with rice or noodles.
«The beef can be marinated well ahead of time. In fact, it can be frozen -raw- with the marinade for a later date.»