Mythbusters! - They completely failed to destroy a microwave, even with spoons, forks, sparking crumpled foil, and many other things.
Not a great idea to do it with the family microwave, and never leave it on for more than the initial flashover, any futher power applied will be going into creating a very hot spot (risk of fire) or reflecting back into the magnetron.
I wouldn't bank on any kind of light, from IR to UV, erasing anything you wanted destroyed - things you wanted to keep, maybe.
The other possibilty, with suitable shrapnel protection, is snapping, or less violently, a hacksaw, drill or hole cutter. If I had a lot of discs to destroy, I'd try to make some kind of foot operated breaker.