Prepare a large pan of boiling water. Add the noodles, then remove from the heat. As they start to soften, use a fork to unravel them. Cover with a lid, and leave for about 7-8 minutes, stirring occasionally. When al-dente (firm to the bite), tip into a colander and rinse under the cold water tap to stop the cooking process. Set aside.
Prepare the sauce by whisking together the soy sauce, sesame oil, water, sweet chilli sauce, and vinegar in a small bowl. Set aside.
Heat 1 TBSP oil in a large non-stick frying pan (skillet) over medium-high heat. Add the tofu cubes and toss to coat in the oil. Leave to cook for a couple of minutes or so, until browned on the underside, then flip the cubes over. When browned on the second side, transfer to a bowl and set aside.
In the same pan, add the onion and stir fry until it starts to brown (add a splash more oil, if needed). Add the carrot, mushrooms, cabbage and cashews, and stir fry until the mushrooms have released their liquid and browned.
Return the tofu to the pan and pour in half of the sauce. Stir fry for a few minutes, then add the noodles and remaining sauce. Stir thoroughly to ensure the noodles are fully coated in the sauce, then continue stir frying until the noodles are heated through.
Portion into bowls, and enjoy!