Voting Absentee is easy! Be absent but accounted for.
You can get the voter registration and absentee ballot request FPCA here.
You need to fill it out, sign it, put the address of your local voting office (find the address here) where it needs to be sent, and then fold it and seal it (with tape). You can then mail it at a Spanish post office or drop it off at the US Embassy. If you mail it at the Spanish post office you must put postage on it. If you drop it off at the Embassy, you can go Monday-Friday 8:00am-1:00pm, except Spanish and US holidays.