In with the hero, eating eggs (3)
I believe the answer is:
roe
'eggs' is the definition.
(fish eggs)
'in with the hero eating' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ROE' can be found hidden inside 'with hero eating'.
(Other definitions for roe that I've seen before include "Swift runner" , "Mass of fish eggs" , "If hard, eggs" , "Mass of fish's eggs" , "Caviar" .)