Dividing piece of fish, allow fighter no steak (5,6)
I believe the answer is:
filet mignon
'steak' is the definition.
(filet mignon is a kind of steak)
'dividing piece of fish allow fighter no' is the wordplay.
'dividing' is an insertion indicator (inserted letters divide the word).
'piece of fish' becomes 'fin' (fish have fins).
'allow' becomes 'let' (synonyms).
'fighter' becomes 'mig' (fighter jet produced by Russian company MiG).
'let'+'mig'+'no'='letmigno'
'fin' enclosing 'letmigno' is 'FILET MIGNON'.
(Other definitions for filet mignon that I've seen before include "steak" , "Tender piece of beef" , "Small tender boneless cut of beef" .)