There aren't a lot of restaurants on the hill. Sweet Basil
has a food cart on SW Gibbs and they offer a number of vegan options. I've found the cafes on campus to be quite vegan friendly and the food is not bad tasting either. The cafe on the third floor of the OHSU hospital has pretty good vegan options most days and a good salad bar. I'm mostly familiar with the Mac Hall cafe and they almost always have a vegetarian soup that is frequently vegan (and labeled as such). They also have vegan entrees fairly often.
You can look at some of the menus here: http://www.ohsu.edu/food/retail.htm
The website is kind of crepe, but it gives you and idea what's available.
If you're willing to go off the hill there are lots of vegan options near PSU.