It's eaten, sir, possibly with fish (7)
I believe the answer is:
rissole
'it's eaten' is the definition.
I can't judge whether this definition defines the answer.
'sir possibly with fish' is the wordplay.
'possibly' is an anagram indicator.
'with' says to put letters next to each other.
'fish' becomes 'sole' (sole is a kind of fish).
'sir' is an anagram of 'ris'.
'ris'+'sole'='RISSOLE'
Can you help me to learn more?
(Other definitions for rissole that I've seen before include "faggot" , "Sil rose for the meatball" , "Small pastry" , "Croquette" , "Minced meat or fish deep fried in egg and breadcrumbs" .)