beef chow mein

2 wholemeal noodle nests (85g) 2 tsp rapeseed or sesame oil 200g lean fillet steak, fat removed and cut into strips 1 small red onion (100g), finely chopped 15g piece of ginger, peeled and finely chopped 160g chestnut mushrooms, thickly sliced 2 garlic cloves, finely chopped 160g ready-to-eat beansprouts 1½ tsp tamari 1 tbsp brown rice vinegar 4 spring onions (65g), cut into diagonal lengths thanks watching