Filling sole, say, with glue (9)

'filling sole' is the definition.
The answer and definition can be both things that one consumes for nourishment as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'with glue' is the wordplay.
I cannot really understand how this works, but
'glue' could be 'paste' (synonyms) and 'paste' is found within the answer.
The remaining letters 'fish' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

'say' acts as a link.

Can you help me to learn more?