Sprinkle onto the dish, when one's messing about (6)
I believe the answer is:
season
'sprinkle onto the dish' is the definition.
I can't tell whether this defines the answer.
'when one's messing about' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'messing' is an anagram indicator (I've seen 'mess' mean this).
'about' indicates putting letters inside.
'ones' with letters rearranged gives 'seon'.
'as' placed within 'seon' is 'SEASON'.
Can you help me to learn more?
(Other definitions for season that I've seen before include "To dry (wood) for use as timber" , "Eg, summer" , "Add taste to; part of year" , "instruction in recipe" , "Add flavouring" .)