Portland Mercado! Most, if not all, of the trucks are vegan-friendly. It's a food truck start up program by Hacienda CDChttp://www.portlandmercado.org/
Verde Cocina, who has 1 or 2 locations and a good stop for food if you are the Portland Farmers Market (Sat). Super fresh veggies and ingredients.
In Portland, unless you seek it out, the tacos are going to be a bit more about amazing NW produce...
3 sisters tortillas & masa are really great - you can get them at New Seasons and the Peoples' Coop (and they sell them fresh at the Wed. weekly market outside).
I don't know the names, but there are a bunch of Mexican markets and even a supermercado or 2 in Hillsboro, outside Portland.