One major rule with microwaving....Use glass containers. Alot of talk about plastics leeching into the food. Also, I try to avoid the microwave, but for a quick reheat 15-20 seconds wont make your food useless.
The key thing I do is go with cold meals for work usually. And as for it making the food useless, improbable. I have used very healthy microwave meals and grew well!
That being said, I am trying to get them to let me bring an extension cord and let me use my georgeforman grill at work
I used to use a foreman grill for lunch at one job. 90% lean beef patties with cottage cheese, flaxseed whole grain bread, green beans, and a cup of green tea.
I was envied. Then again I also did dips on chairs, and push ups for my breaks back then...