I'm not really sure what you mean by "historical evidence" for the last supper, it's not as if we have archeological remains of the disciples' plates and napkins or anything. If you want to know why it's a given that Leonardo was painting the Last Supper of Christian theology, it would be because Leonardo was a Chrisitan painter in a Christian context who was painting a popular scene from the Bible. The motif of Jesus and his disciples sitting around a table having their last meal has been a common subject in Christian art since at least the 6th century, and it was obvious by Leonardo's time that he was simply painting his own take on the scene, not referencing some obscure passage from the Quran (which Leonardo Da Vinci almost certainly had not read). Furthermore, the Last Supper is referenced in Paul's letter to the Corinthians which is dated to the 50s AD, roughly 20 years removed from when the event supposedly occurred, while the Quran was not revealed until the 7th century AD. It is wholly unreasonable to assume that the Quran is preserving a detail of the Last Supper that was lost to history given that Paul's letter and the Canonical Gospels, which predate the Quran by hundreds of years, have no mention of a miracle regarding the food being sent by God, and theologically there should be no reason why the authors of the Gospels would not include this miracle, given that the books are full of Jesus and Gid performing miracles, including food-based ones.