We were recommended the Sternen Grill; Theaterstrasse 22, Bellevue, 8001 Zurich; 044 251 49 49;
www.vorderer-sternen.ch <http://www.vorderer-sternen.ch> which is a bit more than 2 blocks, but certainly walkable in a few minutes. There is an indoor section (2 or 3 floors and some terrace table) where it is a normal restaurant. Then there is a fast food type of extension where people just buy bratwursts and sit down with a beer. We tried the former. Would not say it was stellar but was alright.
Nearby is the Odeon, which we were told used to be a cafe/bar for intellectuals.
For fondue, we tried la dezaley -
http://le-dezaley.ch/ is walkable but please make sure you get clear instructions as the entrance is slightly obscure. We told it is considered one of the best in Zurich. We are cheese and fondue fanatics. We find the fondue here good, but not the best from experience.
Happy eating!