The most important thing when cooking seafood in the microwave is to remember that it cooks very quickly, so err on the side of caution in your cooking times. It is better to undercook then return the food to the microwave for another blast, than to spoil a dish by overcooking.
You can use all kinds of fish for your mug meals but firmer-fleshed varieties will hold together best. Be careful, when stirring, that you don’t break up the fish too much.