1/2 cup water
Pinch of salt
Use a mug or bowl that holds 1 cup or more. Put the water in it, add the salt, crack the egg into the water and make sure it is submerged.
Cover the top of the mug and zap on high power for one minute. Remove from the micro; see if the white is firm. If it needs more cooking, put back into the micro and zap for 15 seconds. Repeat if necessary, although it shouldn't be unless your micro has very low power. When the egg is ready, remove with a slotted spoon. Season as desired.
Please note: You have to find the right time in your micro. If it goes too long, there will be a mini egg explosion... That's also why it's good to use a saucer or something to cover the top of the mug.