I found it ridiculously hard to find a TESOL course that was offered in Hanoi. All the courses seem to be in HCMC. I did manage to find one though. It was a 5 day course and crazy easy to get your certificate.
So if anyone is looking for a school that provides TESOL courses in Hanoi, shoot me a message, I'll bring you to their door. As a matter of speech. Not literally.