If you are looking for a great vietnamese food try:
1901 NE 39th Avenue
(located in a strip mall next to baskin & robbins)
It has been a favorite for my family for about 5 years. I have been through a fair amount of the menu. I find that when I go there I am usually craving a dish that I have on a previous experience but every time I branch out and try something different it becomes my new favorite dish. This place is incredible! All of their vegtables are fresh and never overcooked and you can get dishes as spicy as you can handle.
I currently relocated to New York. I plan to come back to Portland for the holidays and My-Cahn is on the top of my list of places to go.
Some quick recomendations. Lemongrass Chicken, Mongolian Beef, Stuffed Eggplant (pork, chicken, etc.), Hot & Spicy Soup, and just about anything else you can point to on the menu!