Beyond in Zurich is pretty good for steamed buns ('xiaolongbao'.. somewhat similar to the dim sums that you might be looking for?) and Sichuan (spicy food). Right next to Zurich HB.
I can recommend Nagasui in Zürich. It is not specifically chinese, but asian in general but it was the best asian restaurant I have visited in Zurich so far.
If you don`t mind a little waiting time and a very crowded place, I can also recommend Lilys in Langstrasse. The tables etc are very minimalistic and you have to share the tables with other customers (they only have long tables with 16 seats or so), but they have the best Thai currys I ever had in Zurich. I can especially recommend the green one with Thai aubergines.
beijing town in montreux. a lot of students eat there so it is "cheap" but also a lot of the students are asian and they keep coming back so it must be good
canard pekinois in lausanne is really good (at least by my standards). the speciality is... peking duck
banana leaf in geneva. again a student place but the 3-course duck menu is amazing. went with a friend from hong kong and he vouches for it
Lily's is awful, it is not authentic Thai at all so if it's the best curry you have had then I suggest going to a good restaurant like Ah Hua near Helvetiaplatz.
Did they ever claim to be authentic Thai? I remember them having Myanmar stuff in there, but that's years ago. I guess all South East Asians in Europe will call their stuff Thai food as it simply sells better. Even all Vietnamese places in ZH seem to put Thai curries on the menu cause people keep on asking for them. Hard to believe that one of the most populous regions of the world could offer more than the same green chicken curry again...
Just as you will find in Europe loads of "Indian" restaurants and no Pakistani... outside of specific places in the UK where the muslim community is so strong that it works again... (if that does not start a Friday discussion I don't know what would...)