Tempting, half-decent, cake covering! (8)
I believe the answer is:
enticing
'tempting' is the definition.
('entice' can be a synonym of 'tempt')
'half-decent cake covering' is the wordplay.
'half' indicates taking half.
'cake covering' becomes 'icing' (I've seen this before).
'decent' with half the letters taken is 'ent'.
'ent'+'icing'='ENTICING'
(Other definitions for enticing that I've seen before include "Having an allure" , "Luring" , "Attracting by offering pleasure" , "Alluring" , "Tempting or beguiling" .)