Heat the oil in a wok, deep frying pan or non-stick pot until it's almost smoking. Throw in the carrot or sweet potato and keep it moving around the pan for 90 seconds. Add the peppers and cook for 2 to 3 minutes, then add the pak choi, green beans and sugar snap peas and cook for 1 minute more. Add the shallot, garlic, chillies, if using, and the ginger and cook for 1 minute, stirring constantly so that nothing sticks. Pour in the sauce, then add the cooked noodles and toss everything together until well combined.