You are using the rails gem and you have a Router:
App.Router.map ->
@resource "things", ()->
@resource("thing", path: ":thing_id", ()->
@route "create"
You want to make templates for "things", "thing" and "thing/create", but you are using seperate files and don't know where and how they should be structured.
Rule of thumb: resources are not nested, but routes are. Meaning you put all the the templates associated with "resources" at the top level and the rest in the resource it routes to's folder:
./things.hbs
./thing.hbs
./thing/create.hbs
This applies no matter how far into the nested chain you would go.