At this food court, first go to one of the round desks and buy a card for 100 baht. They will reimburse you for whatever you didn't spend. Use this card to pay at the Vegetarian food stand -- I didn't know any of this and gave them cash and they took it, but that was the wrong way.
I first went on Sunday around 3pm and the Vegetarian Food stall (along with many others) was closed.
The food was alright. I tried five options. Two were tasty (but not fancy, simple and tasty). I tried what I think was batter-fried mushrooms, although it was almost entirely batter with the occasional tidbit of mushroom, not a fan. I also tried something that looked like mock meat, but it was hard, like eating chips, and not much flavor. So, you point to what you want and take your chances. I asked the person working there what she recommended, and she just said it's all good.
But it was cheap (35 baht for two choices with rice), and tasty enough, I'd come again.
On a weekday around noon it was very crowded. I was able to find a seat, but it took quite a bit of wandering.