I recommend going with mushrooms that have a good chew to them, so anything except button mushrooms generally work; this will be the "meaty" component. Some crunchy vegetables will add freshness, such as sugar snap peas, celery, or bell peppers. I also like to add pressed tofu; which for this recipe I buy the marinated kind, but the plain one will work as well since the noodles are quite flavourful. You can also get extra firm tofu, but be sure to fry them first to get a crust on them.