If you have your freezer meals in plastic containers, it is definitely tempting to pop the entire thing into the microwave to defrost and/or reheat the meal. It is convenient, but new health information is definitely advising against this method of heating up food.
The safest way to reheat or defrost meals in the microwave is to place it in a microwave-safe casserole dish or in a microwave-safe glass bowl. This means you do not have to worry about chemicals being leached into your food when the plastic is heated. You should also avoid using plastic wrap whenever possible as well.
It should be obvious that no plastic containers should go in the regular oven for reheating!
And as an added bonus, you are helping the environment too, by not using disposable or semi-disposable plastic containers.