Just Oliver perhaps, eating gruel finally (6)
I believe the answer is:
hardly
'just' is the definition.
(I know that just can be written as hardly)
'oliver perhaps eating gruel finally' is the wordplay.
'oliver perhaps' becomes 'Hardy' (as in Oliver Hardy from Laurel and Hardy).
'eating' is an insertion indicator.
'finally' says to take the final letters.
The last letter of 'gruel' is 'l'.
'hardy' going around 'l' is 'HARDLY'.
(Other definitions for hardly that I've seen before include "Not quite "It seems unlikely!"" , "Almost not" , "Barely, scarcely" , "With great difficulty" , "Not much" .)