Outspoken, very, on coal production (5)
I believe the answer is:
vocal
'outspoken' is the definition.
(I know that outspoken can be written as vocal)
'very on coal production' is the wordplay.
'very' becomes 'v' (abbreviation).
'on' means one lot of letters goes inside another.
'production' indicates anagramming the letters.
'coal' anagrammed gives 'ocal'.
'v' inserted within 'ocal' is 'VOCAL'.
(Other definitions for vocal that I've seen before include "Relating to the human voice" , "(Performance of) piece that is sung" , "singing" , "not instrumental" , "Outspoken (e.g. criticism)" .)