Preheat oven to 200°C. Chop onions roughly. Cut mushrooms and stems roughly. Combine soy sauce, sesame oil, salt, crushed red chillies and vegetable stock in a bowl.
Cut aluminium foil into 8 inch squares and take 2 squares per pouch. Place some boiled noodles in the centre of one pair of foil squares, top it with a portion of mushrooms and onions. Gather the four corners of the square and bring together to make a pouch.
Pour some of the spiced stock into it. Seal the edges loosely. Make 4 such pouches. Arrange these pouches on a baking tray and cook in the preheated oven for 10-15 minutes. Serve in the foil itself.