About to express disapproval of extremely sparse galley (7)
I believe the answer is:
caboose
'galley' is the definition.
('caboose' can be a synonym of 'galley')
'about to express disapproval of extremely sparse' is the wordplay.
'about to' becomes 'ca' (I've seen this in other clues).
'express disapproval' becomes 'boo' (I've seen this before).
'of extremely' suggests removing the centre (I've seen 'extremely' mean this).
'sparse' with its middle removed is 'se'.
'ca'+'boo'+'se'='CABOOSE'
(Other definitions for caboose that I've seen before include "Kitchen on ship's deck" , "American at the rear" , "US train crew's accommodation" .)