This one is obviously a bit of a stretch, but here goes:
With a POD of no later than Yarmouk, have the Byzantines discover and settle the Americas (say that sometime during the Justinian Era the Byzantines start to scout the Atlantic Ocean, maybe in an attempt to find a sea route to China). I don't know much about the endurance of period Byzantine vessels, so I'll allow for a few sudden advances in Byzantine naval technology.