Hi Tracey,
I have mushroom chow mein from my chinese takeaway (i'm not veggie but I love this!) and I class it as free...
Not sure if it is but a chicken chow mein is 6 syns on green for the chicken so I think mushroom chow mein should be free, after all it's mushroom, onion, beansprouts and noodles - no gravy just some soy sauce.
Hope this helps!