I was overjoyed when I found Tibits right around the corner from my hotel. After visiting a number of Swiss restaurants that claimed to be vegetarian-friendly (only to find that the only vegetarian items on the menu were covered in cheese), I happened upon Tibits, which not only has approximately half of its buffet options marked with a "V" (for vegan) but also has a few vegan desserts.
The food is not haute cuisine but there's a lot of variety and the prices are reasonable. Most of the food is buffet-style although there are some entrees that can be ordered at the counter. I had some falafel, potatoes in mustard sauce and a couple of tofu dishes. For dessert, there was a vegan apple tart (which was delicious, I might add) and many flavors of sorbet to choose from. Tibits also has a great selection of tea, coffee and juices. The inside part is (what seems to be) one of the few non-smoking restaurants in Zurich.