Is it possible to have Google Assistant work with screen off? When I'm out and about, I usually have wireless headphones (with mic) on, and my phone in my pocket, usually listening to a podcast. 

Quite often I want to add something to my todo list- and I'd like to have Google Assistant do that for me. 

But the problem is that it seems that Google Assistant requires screen on to work - is it possible to get around this?
To use Google Assistant with features as shown in this article on Google Assistant headset instruction videos you'll need to be using Headphones optimized for the Google Assistant or Made for Google:

See: Official Google Assistant on Headphones Documentation