i have been freezing avocados for a while.
since they are the one thing around here that only fruits once a year.. i get longing for avocados in the summer.

i just take ripe avocados.. put them in a freezer bag and smash them by hand.. simultaneously pushing the air out of the bag.
i have some that are 3 months old and just as green as when i put them in the freezer. no lemon juice no acid.

if you do it with a rigid container.. of course it wont last in the freezer head space makes freezer burn. but the avocados dont seem to expand one bit when frozen so maybe a vacuum dealy rigid container would work.