Not that easy. They don't eat so many vegetables, in most dish, there is only little tiny pieces. I don't know how many times I ended up eating plain rice with just an egg (i am vegetarian not vegan) because they could not make up anything else without meat or fish xd
many Thai food restaurants put lots of sugar, msg and other things that are bad for health, especially on the long term and dishes are in general not well balanced in terms of type of ingredients (almost no veggie, mainly carbs)... So if you pay attention to your health or are a vegetarian, it is really really a big struggle here to eat local.