We could try Wild Abandon restaurant on Tuesdays
http://wildabandonrestaurant.com/
map=
http://www.urbanspoon.com/u/map/284074/restaurant/Southeast/Wild-Abandon-Portland
The food is reputed to be excellent, has an outdoor patio. They are normally closed on Tuesdays, however, I know of one other meetup group they opened for on Tuesday and ran a happy hour menu. So the prices were great and the reviews were excellent. I do not know if they can accomodate a younger crowd. Possibly during the day. I think we would have to promise them 30 people or more to open up.