Characters inside school getting cooked salmon (4)
I believe the answer is:
coho
'salmon' is the definition.
(type of salmon)
'characters inside school getting cooked' is the wordplay.
'characters inside' indicates the central letters.
'getting cooked' indicates an anagram.
The central letters of 'school' are 'choo'.
'choo' is an anagram of 'COHO'.
(Other definitions for coho that I've seen before include "Fish" , "Small north Pacific salmon" .)