There are very few vegan stalls. One stall sells vegan fried rice which is very delicious and not oily at all. There is fried vegetables with large noodles but it is slightly oily. They also have other Thai Chinese dishes and desserts. Made fresh every Tues-Fri. Cash only and very cheap.
The other stall I found sold vegan Thai fruit and vegetables drinks such as pumpkin, corn, etc. Drinks are either piping hot or cold. Made fresh every Tues-Fri. Owner tends to come in around 7 am.
If you walk around, some stalls may sell some vegan dishes. One stall sells hot soy milk and desserts that you can put into the hot soy milk.
Fresh vegetables and fruits are also sold.
Some stalls are there early, around 6 am.
Cons: stinky area