Iran (and the NorKs) wants to nuke America so it can’t protect Israel anymore. What better way of delivering the payload than with a 777? And you don’t even have to miniaturize the nuke. All you have to do is squeeze it through the door.
Re-paint it, hack the flight computer to make it look like another 777 aircraft, file a fictitious flight plan and away they go!
Not as crazy as it sounds, as Burma is along the plane’s range and Burma is an ally of both Iran and North Korea.