Thank you for your message. It may be possible to do this as Linux is very flexible this way, but we do not have particular code or steps that would accomplish this.
A lot in this answer depends on what you may be trying to do. Is it just a one-time connection with a known device when the Zero is booted? Are you trying to connect and disconnect multiple unknown devices at a kiosk or something similar?
Generally a known device can simply reconnect without going through an authentication process.
For other host devices that could initiate the connection (such as a phone), it may be as basic as automatically accepting pairing attempts that are received by the Zero and having the Zero remain discoverable.
If your goal would be to have the Zero automatically initiate a pairing with an unknown device, this would likely be much more difficult to implement. It would essentially require the Zero to perpetually scan for available Bluetooth devices and make pairing attempts with devices that aren’t connected which isn’t likely to work well.
Ultimately the best answer may be to experiment with it and see what is possible.
I hope this helps.