Streamlined dairy came on post-restructure (11)
I believe the answer is:
aerodynamic
'streamlined' is the definition.
(streamlined for travel through air)
'dairy came on post-restructure' is the wordplay.
'post-restructure' is an anagram indicator (after restructuring).
'dairy'+'came'+'on'='dairycameon'
'dairycameon' with letters rearranged gives 'AERODYNAMIC'.
(Other definitions for aerodynamic that I've seen before include "Fit to be a high-flyer" , "Having a drag-reducing shape" , "very good on air?" , "Designed like a bird" , "could be made to fly?" .)