This plugin does not offer the capability to send push DATA notifications.

Can you deploy a new version with this capability?

This is very easy since the api you are consuming already offers this capability with the usage of "PostNotificationsRequest.Data" attribute.

At least you could make a change on the "PostNotification" action, add an input parameter "Data" with the structure "Data" from Onesignal REST service and set it as public.
This way we could extend the OneSignalAPI on our apps to send the required push data notifications.

Thanks,

Tiago Peres