Cheese often that is oddly overlooked (4)
I believe the answer is:
feta
'cheese' is the definition.
(I've seen this before)
'often that is oddly overlooked' is the wordplay.
'is oddly overlooked' means one should take alternating letters.
'often'+'that'='oftenthat'
The alternating letters of 'oftenthat' are 'FETA'.
(Other definitions for feta that I've seen before include "Greek salad cheese" , "Greek sheep or goats' cheese" , "Greek cheese from goat or sheep milk" , "Low-fat cheese" , "food there" .)