Hors d'oeuvres topping (3)
I believe the answer is:
roe
'hors d'oeuvres topping' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for roe that I've seen before include "shy animal" , "A mass of fish-eggs" , "eg Caviare" , "Food from fish" , "Caviar" .)