I found this on the site....
December 2005 - Freezing Banana & Avocado
Myth: You can't freeze Bananas and/or Avocados
Truth: We are unsure where this myth originated however we suspect it may
be perpetuated by parents who have had their banana and/or avocado turn
brown when frozen. There is no health/nutritional reason for not freezing
bananas and/or avocados.
True, they may turn brown however this browning is natural and unless you began with brown and rotting fruit, the browning is not indicative of rot. Browning is the natural process that occurs as many fruits oxidize and ripen.