I've experimented quite a bit with the various vegetarian meal options on transpac C, and the best option I've found is, when asked for your meal choice, say:

"I requested a vegetarian meal when I booked the flight, did it not show up?" Then look really disappointed and sad.

The half a dozen times my meal request didn't make it into the system, the resulting FA improvisation (modifying existing meals, getting stuff from F, or whatever they do) has been 100% better than the normal appalling vegetarian meals I've received.

The only good Indian Veg meal I've ever had was from LHR, and it was good. Almost every other time they seem to substitute the vegan meal, which is bad news for dessert. And I agree that the catering services at Bangkok (especially TG, which may use the same people) can put out some shockingly bad stuff.