Very big award presented by Asher on occasion (5)
I believe the answer is:
obese
'very big' is the definition.
(I've seen this before)
'award presented by asher on occasion' is the wordplay.
'award' becomes 'OBE' (Order of the British Empire).
'presented by' is a charade indicator (letters next to each other).
'on occasion' means one should take alternating letters.
The alternate letters of 'asher' are 'se'.
'obe'+'se'='OBESE'
(Other definitions for obese that I've seen before include "Having excessive girth" , "Very big" , "Morbidly fat" , "Abnormally fat" , "getting well-upholstered" .)