To cook it through, I take the ends off the potato and stab it a few times to let the steam escape while its cooking. Then I zap it for 3 and a half minutes on one side, and 3 and a half on the other side. This is for a pretty average potato so if you get an absolute monster you might want to up the time to five minutes or just cut it in half. After its cooked through I tend to do one of a few things with it:
Blend it to make soup/smoothie. I quite like adding a bit of plain yoghurt, salt and pepper to make a savoury smoothie soup thing, its pretty good for straight after gym sessions.
Fry it - this is the less healthy option, but if you have a non stick frying pan this is awesome. Cut it up into chip sized bits and dry fry them until crispy on the outside, like sweet potato fries!
Cube it up and put it in a salad. This adds a meaty element to many a boring salad, I quite like stir frying bean sprouts and adding them.
If you like humous, add it to sweet potatoes. It works really well if you just want something quick, I just cut the whole thing in half and add a massive spoonful. Or dollop humous onto my salad. Or just dipping it in general.