From website Naval Scran -----

The Objective of the following list - Is to recall the common names by which various items of food were or are known on the mess deck ...

Chicken on a raft
c.1940 -
c.1970s         Egg on toast

I am perfectly conversant with Cyril's glossary, thank you Bill. My point is that his usage is not definitive ~~ see e.g. the authoratitive source above. Look at the thread title, please. We are discussing the phrase's meaning, not merely one singing seaman's usage of it.