Strong point in favour of unfinished meal (5)
I believe the answer is:
forte
'strong point' is the definition.
(I know this)
'in favour of unfinished meal' is the wordplay.
'in favour' becomes 'for' (as in being for a particular cause).
'of unfinished' means to remove the last letter (I've seen 'unfinished' mean this).
'meal' becomes 'tea' (tea is a type of meal).
'tea' with its final letter removed is 'te'.
'for'+'te'='FORTE'
(Other definitions for forte that I've seen before include "In music, to be played loudly" , "Thing at which one excels" , "Musically, loud" , "Strong point - loudly (in music)" , "Strength" .)