You can nuke it, we're not maniacs. However, we recommend reheating your previously cooked pasta in a large pan wide enough to hold the pasta in an even layer. Add a small quantity of water to the pan before adding anything else, heat it until it's simmering on the edge, and add your already cooked pasta/sauce. Use a wooden spoon or spatula and swirl the pan around in a circular motion over the heat. Add water if necessary, but only enough to bring your sauce back to the right consistency. The more water you add, the more your pasta will take it on, too.