Suan Plu Mangsawirat Vegan Canteen
Amarin Plaza's food court is your typical mall collection of eateries, but there's a vegetarian food stall stall worth seeking out if you're in the area around lunchtime. It's not 100% vegan, but it's pretty obvious which dishes aren't suitable (e.g. the stack of eggs). The selection of dishes is reasonable and inexpensive, at around 40 baht for a large plate of food. Also be sure to check out Fresh Up Juice Bar, also in the Amarin Plaza food court, a vegan friendly sweets stall with desserts for around 20 baht.
One of my favourite discoveries, and one I managed to replicate pretty well in my own vegetarian nam prik ong recipe, this rich and salty entrée is highly recommended.
I'm a sucker for Thai sweets, so even if I'm full to the brim I'll still take anything that's available. Fresh Up Juice Bar has a variety of combinations from which you can choose, but I went with a simple bowl of sweet black sticky rice with salty coconut milk. All the love.
If you want a cheap, cheerful, and tasty lunch around Pathumwan or Lumphini then consider the vegetarian options at Amarin Plaza. It's hyper busy at lunchtime, as are most places, but if you can manage a table with a view it's a good place to enjoy some air conditioning and people watching on the streets below.