I just read the question: Does microwaving a hard drive erase it? and now I am curious too... does microwaving a CD (or for that matter, DVD, or blu-ray) erase it? My initial thought is that some data would remain, but that it would largely corrupt the data. Would microwaving the CD completely clear off any data though, including small pieces of data, such as passwords? This is not a dupe because a CD does not have a protective case around it like a hard drive does, so the result will likely be different in the case of a CD.
The aluminium coating of the CD reacts and creates plasma. So it burns the CD effectively. Below you can see the image of a microwaved CD. It's safe to say it's been destroyed.