London Eye is a treat this time of year (5,3)
I believe the answer is:
mince pie
'london eye' is the definition.
'mince pie' can be an answer for 'eye' (I've seen this before). I'm not certain of the 'london' bit.
'treat this time of year' is the wordplay.
I cannot really understand how this works, but
'time' could be 'min' (short for minute) and 'min' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for mince pie that I've seen before include "Christmas delicacy" , "Xmas treat" , "Christmas treat" , "seasonal fare - with 25d" , "Christmas pastry" .)