I found this nice blog post about bi chay. I don't eat pork but I know pork skin bi is used in banh mi and as a texture and flavor addition in other dishes like com suon plates. Bi chay is the vegetarian version. I am not sure if it was developed for Buddhist fast days or just as another food, but it is crunchy and yummy. The blogger says she uses bi chay for veggie banh mi and goi cuon chay.
How do you use bi chay? Any other traditional ways or innovative ways?
Also, my local Vitenamese market labels their bi chay as bi hop, but it seems to be the same products. Are these two different names for the same things? I know 'chay' is veg, but what is hop?