I turned to the QuickStart Guide (nice, I wish more software came with one) but it misspelled the password command (where do I file a bug?)
You can see the correct options by using
bitnami-lampstack-1.2-0-linux-installer.bin --help
This worked:
sudo /home/mohish/bitnami-lampstack-1.2-0-linux-installer.bin --mode unattended --base_password MY_password