I think we need some sort of PM list to make people aware of upcoming 20 CHF lunches.
A sugestion:
One of my most recent finds and probably the most authentic bibimbap I had in Zurich is just over 20 CHF...
That would be the place
http://akaraka.ch
That have a 19.90 all you can eat lunch buffet twice a week, but I personally found the bibimbap better. Havent tried the spicy soup so far.
The take reservations which was the problem with most snack bars in that price class...