Cooked trout for instructor (5)
I believe the answer is:
tutor
'for instructor' is the definition.
(tutor is a kind of instructor)
'cooked trout' is the wordplay.
'cooked' indicates an anagram (letters cooked into a new form).
'trout' with letters rearranged gives 'TUTOR'.
(Other definitions for tutor that I've seen before include "college teacher" , "train" , "Personal teacher" , "Private instructor" , "Guardian" .)