Originally I had this (abridged):

.
├── html
│   ├── pix
│   │   ├── cc2.png
│   │   ├── dilad.png
│   │   ├── favicon.png
│   │   └── wallpaper_1080x2400.png
│   ├── app
│   │   └── mojo2.fcgi
│   └── robots.txt
├── lib
│   └── MyApp.pm
├── t
└── templates
    ├── MyApp
    │   ├── home.html.tt -> home.tt2
    │   ├── home.tt2
    └── lib
        ├── footer.tt2
        ├── form.tt2
        └── header.tt2

but now I've moved the application mojo2.fcgi up so that it's like this:

.
├── fcgi
│   └── mojo2.fcgi
├── html
│   ├── pix
│   │   ├── cc2.png
│   │   ├── dilad.png
│   │   ├── favicon.png
│   │   └── wallpaper_1080x2400.png
│   └── robots.txt
├── lib
│   └── MyApp.pm
├── t
└── templates
    ├── MyApp
    │   ├── home.html.tt -> home.tt2
    │   ├── home.tt2
    └── lib
        ├── footer.tt2
        ├── form.tt2
        └── header.tt2

and this allows me to use the relative paths ../templates/lib etc in the plugin.

Mojo::Home looks like it might be useful for other things, however, so thanks for the pointer. There's clearly a lot of domain knowledge here which I don't have - and that isn't unique to this framework by a long way.

mojo generate app hippo

generates:

.
├── hippo.yml
├── lib
│   ├── hippo
│   │   └── Controller
│   │       └── Example.pm
│   └── hippo.pm
├── public
│   └── index.html
├── script
│   └── hippo
├── t
│   └── basic.t
└── templates
    ├── example
    │   └── welcome.html.ep
    └── layouts
        └── default.html.ep

9 directories, 8 files

Tutorial explains defaults for static files, external templates and Home among others.