For production Ubuntu Phone devices, adb has been disabled in recovery, and this affects ubuntu-device-flash operation.

You must supply a recovery image with adb enabled, which ubuntu-device-flash will use temporarily while doing its work:

• For BQ Aquaris E4.5 Ubuntu Edition (aka krillin), use recovery-krillin.img
• For BQ Aquaris E5 Ubuntu Edition (aka vegetahd), use recovery-vegetahd.img

ubuntu-device-flash can then be supplied with the --recovery-image argument, eg:

ubuntu-device-flash touch --channel ubuntu-touch/stable/bq-aquaris.en --bootstrap --recovery-image path/to/downloaded/recovery.img

Note that when the command prompts you with:

Expecting the device to be in the bootloader... waiting

You can put a Aquaris E4.5 and Aquaris E5 in the 'bootloader' by holding down Power + Volume Up for a few seconds, releasing the Power button when the red LED lights as the machine reboots, and then selecting 'fastboot' from the device's boot menu.

unknown flag `recovery-image'

If you get this error, that means you are still using an older version of ubuntu-device-flash. Please install the latest version using the ppa

sudo add-apt-repository ppa:phablet-team/tools
sudo apt-get update; sudo apt-get upgrade

your phone, I’m afraid, has the wrong chip set, see also my statement here:
https://askubuntu.com/questions/843973/attention-dont-buy-bq-aquaris-e5-with-a-wrong-chip-set

Volker