Filling search with fake jewels (9)

I believe the answer is:

fishpaste

I'm a little stuck... Click here to teach me more about this clue!

'filling' is the definition.
The definition and answer can be both things that one consumes for nourishment as well as being singular nouns.
Perhaps there's an association between them I don't understand?

'search with fake jewels' is the wordplay.
'search' becomes 'fish' (fishing is a kind of searching).
'with' means one lot of letters go next to another.
'fake jewels' becomes 'paste' (I've seen this in another clue).
'fish'+'paste'='FISHPASTE'

Can you help me to learn more?

I've seen this clue in The Daily Express.

Want a hint initially instead of a full solution? Install my app