Remove the thick layer of fat running down the side of the steaks and discard. Slice the steak into 1cm-thick, long strips and toss with the cornflour and some seasoning.
Heat the oil in a large frying pan or wok over a high heat then add the steak, frying for 3-5 mins or until golden brown on the outside. Remove with a slotted spoon and transfer to a plate.
Add the onion and peppers to the pan and fry for 6-7 mins or until beginning to soften. Stir through the garlic, ginger and chilli and cook for a further min. Return the beef to the pan and stir through the black bean sauce, rice wine vinegar, sugar and 2 tbsp water to loosen a little. Bring to a simmer and then remove from the heat.
Serve the stir-fry in deep bowls with mounds of sticky rice and top with coriander, if you like.
