My answer then would be not very. Different states have different requirements, but every district I've encountered has expected teachers to be eligible for a certificate before hire. Maybe Oregon has some sort of a short-term provisional certificate? Since you've been teaching overseas, do you have a teaching certificate issued from a different locale? There may be options for reciprocity. You also might have luck if you talked to district HR departments. Schools who receive Title I funding couldn't hire you without being eligible for a certificate, but other schools have more leeway.