Well, I know for a fact that iguanas love lettuce, since I took care of one a while ago. Next, unless they're assholes, I don't think your neighbors would leave their iguana home alone if he couldn't take care of himself. Maybe putting him back in the house would be a solution. Also, where do you live, because if where you live is cold, you should take care not to leave him outside. Also, Iguanas are nice and pacific creatures, so he won't try to hurt (eat) you, no matter how big he is.