Roly-poly left in grill (5)
I believe the answer is:
plump
'roly-poly' is the definition.
(I've seen this in another clue)
'left in grill' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' is an insertion indicator.
'grill' becomes 'pump' (both can mean to interrogate).
'l' placed into 'pump' is 'PLUMP'.
(Other definitions for plump that I've seen before include "Not obese, just pleasantly rounded" , "stout" , "Opt - round" , "Rotund" , "Slightly fat" .)