I have weighed my Beef in Black bean portion from my local Chinese restaurant to check how it compares to the portion mentioned in the Syns section of the SW book.
I was pleasantly surprised to find that the portion is only 400g (which I find is more than enough).
The Slimming World book states that it is 8 syns for an average 550g portion.
Always check for updated syns values. Syns values correct at time of posting.