Free lunch includes fish (3)
I believe the answer is:
eel
'fish' is the definition.
(eel is a type of fish)
'free lunch includes' is the wordplay.
'includes' indicates the answer is hidden within the clue.
'EEL' is hidden in the letters of 'free lunch'.
(Other definitions for eel that I've seen before include "Conger, e.g." , "Slippery figure" , "A sea snake" , "Evasive type" , "Creature like conger or moray" .)