can you microwave raw onions in a microwave?!

If you microwave onions, you won't be browning/caramelizing them, you'll be steaming them. That will cook them but they won't have that extra flavor of the caramelization. I do that all the time just to soften onions separately to add to another dish I'm preparing (like making the filling for an omelet, in which case I'll cut onions and celery up small, and shred a carrot to microwave together).

I don't think that the skin of an onion is air-tight enough to cause an explosion when microwaved (like a yam or eggshell), but you could certainly pierce one a few times to prevent that, or cut the onion in quarters or something.

You'll generally want to put the onion in a covered container or wrap with plastic wrap (though I avoid heating plastic wrap myself) or with waxed paper or parchment paper if you don't leave the skin on though since the onion could dry out too much by the time a the whole thing got cooked all the way to the center in a microwave.

P.S. Do NOT wrap the onion in aluminum foil for microwaving, since metal blocks microwaves (that would be appropriate in a regular oven though).

Yeah, you can microwave onions, but it will only ruin their flavour.
Make sure to pierce the skin before you do though.

Try wrapping in foil and baking until caramelized.