My top lunch picks near the Hauptbahnhof (I also work in the area):
1. Saigon, Sihlstrasse (Vietnamese) about CHF 20-30 for meal + drink
2. Asia Cafe, opposite Paddy Reilly's, Sihlstrasse (lentil and massaman curries are great, about CHF 17 for a vegetarian meal and they also have meat dishes. It all sits in heated trays all day so don't go for something that doesn't get better over time!)
3. Hiltl. OK but expensive, and I don't think many of the individual components are actually top-class.
4. The Chinese place in the Hauptbahnhof underground where it goes up to meet Bahnhofstrasse. CHF 9.50 for a plate of fried vegetable noodles with their utterly addictive sweet-hot-chilli sauce. I've tried other fried noodles and chilli sauce in Zurich but those are the best.
5. Wagamama. At least CHF 22, but free green tea and you can sit by the river if you go outside peak hours on a nice day, and the food is above average for Asian in Switzerland and cooked fresh.
6. The falafel place on the pedestrian zone that Seidengasse turns into. Not sit-down but really nice fresh falafel.
Any suggestion on authentic thai food in Zürich / Zug? I don't mind if it is an eatery, point is it must be real thai. There is one in Basel at Claraplatz but unfortunately we are not frequent there any longer.
Ploy Thai on Uetlibergstrasse (Zurich Binz area) is a Thai restaurant run by Thai people - if you tell them you like the food spicy they will do it with a Thai amount of chili (rather than the less spicy version that appeals to the local palette). They are also really friendly and speak English pretty well.