Koh Lipe, an island away from everything, while not exactly known as a vegan mecca, has a few good options for those who eschew animal products. The beach restaurant at Castaway Resort gets my vote for the top grub spot (although it is pricey) because they absolute understand what "vegan" means and they dish up some mean cuisine.
Looking back on my notes about their deep fried som tam, I've pretty much written nothing to lend to an actual description of value ("OH. MY. WOW." are the exact words). Som tam is a Thai favourite you'll find all over the place in its conventional form, as a seductively irresistible green papaya salad. But deep fried? Yeah, wow is right. The end result was a garlicky plate of crispy battered and fried papaya served atop a tangy sauce. The snake beans traditionally added to som tam were only lightly cooked (if at all).
Also from Castaway, the fried chicken with cashew nut was veganised for me by replacing the chicken with free range, organic beef.
Psych. It was tofu, and full of wonderful salt and vegetables. All of the dishes, or so they claim, can be made vegetarian (score)!
This coffee was nothing special, but that view every single morning while I woke up!
Available all over the place, mango sticky rice was my breakfast of choice on Koh Lipe every morning. You can't go wrong with it (Thai mangoes are unlike any other), it's cheap, and it's pretty much guaranteed to be vegan.
It's a tiny place, Koh Lipe, and as such the options are fairly limited. Or that's what you'd think, anyway. In reality there's plenty for a plant eater, and anyway you'll probably just end up eating the deep fried som tam for every single meal.