Phones don't really work mounted on a bike, but a simple display could do the job. Sort of how android watch displays an arrow, but using a low power screen.
[1]: https://www.kickstarter.com/projects/1598272670/dashbot-a-49...
However it takes about 10 seconds for the screen to dim to the monochrome power saver mode and then it's impossible to see anything during daylight.
Android wear does not support a permanently on screen all the time and I would totally buy a cheap device like that just for navigating.
Edit: Oh well, android only.
Need to make sure you've got Maps installed on the watch -- I just realised the reason mine stopped doing that was that I didn't reinstall it after my last factory reset.
Buy a Pebble? I have been using a Pebble 2 SE for over a year and one of the primary use cases is so I can navigate on motorcycle.
I leave phone in my pocket. I set the route, maps sends a notification before turns and the watch picks it up. Works in full sunlight and I shake it at night to light it up.
Gets 5-6 days of battery life, I think I paid $40 for mine.
Much easier to process this than the full map on something like my phone or the map on the center console.
It's a shame the dash screen doesn't work with android auto though. (I understand, logically, that the dash and the android auto stuff are separate systems, but it'd be nice...) Nissan actually has pretty good maps, but they're rather ugly (and not quite as good as Google's).