I had dinner at Pot au vert the other night. Very good food - well made, eclectic, interesting. Decent wine selection, good salad bar and soups as well as entrees.
All items are vegetarian, but not vegan - lots of use of dairy and eggs. Menu doesn't label what is vegan but the waitstaff seemed knowledgeable and made recommendations.
Entrees between 15 and 25 CHF, starters less.
Nice ambiance - window tables looking back out at the river and main square across from the train station. Could be a bit noisy, I suppose, though the restaurant is on the second floor.