Don't allow a learner to be unimaginative (5)
I believe the answer is:
banal
'be unimaginative' is the definition.
(thesaurus)
'don't allow a learner' is the wordplay.
'don't allow' becomes 'ban' (I've seen this in other clues).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'ban'+'a'+'l'='BANAL'
'to' acts as a link.
(Other definitions for banal that I've seen before include "Trite and insipid" , "'Trite, time-worn (5)'" , "flat" , "Lacking originality" , "Obvious and boring" .)