If you give yourself a little lead time, it's a lot easier, more economical, and better for the environment to defrost your frozen food naturally. Most foodstuff will defrost thoroughly at room temperature over a 24-hour period, although you may need to allow extra time for very large cuts of meat. Plan ahead. Get whatever you're going to need for your evening meal out of the freezer the night before. If you forget, place your food in saucepan of warm water in the morning.
There's no reason you can't reheat your leftover food in a conventional oven or a saucepan on your stove as opposed to using a microwave. If you time it right, there's little chance of ending up with a cold center to your meal or your food being too hot to eat as can happen with microwaved food.
It can be hard to judge when water you're boiling in a microwave has reached boiling point. The speed at which microwaves heat water means that you won't see the bubbling effect you're used to seeing when water is boiled using more traditional methods of heating. This can result in water being overheated without your knowledge. Using a kettle or a saucepan on a stove to heat your water will not take much longer than using a microwave and is considerably safer.
Most microwave meals include heating instructions for conventional ovens. Even those that don't can easily be cooked in your oven or on your stove top if you remove them from their packaging. Your food is also more likely to be evenly cooked when using a conventional oven as opposed to a microwave.