The mircrowave can work nicely too if expense is a problem and you also do not want another appliance to move around.
I take a large plastik bowl, in the bottom i put the hottest water from the tap possbile. I take a small, cheep plastik plate that is small enought to fit down inside the big bowl, but not small enought to go all the way to the bottom of it. It catches halfway down, leaving a space above it and below it where is the water. I also made holes in the plate to let the steam come up. I put my food on top of the plate and cover with plastik wrapping, with one or two holes made in it.
It works and is inexpensive and all i had to buy to do it was the little plastik plate.