Rodent eating unusual brie dish (7)
I believe the answer is:
rarebit
'dish' is the definition.
(rarebit is a kind of dish)
'rodent eating unusual brie' is the wordplay.
'rodent' becomes 'rat' (rat is a kind of rodent).
'eating' is an insertion indicator.
'unusual' indicates an anagram.
'brie' with letters rearranged gives 'rebi'.
'rat' placed around 'rebi' is 'RAREBIT'.
(Other definitions for rarebit that I've seen before include "Toasted cheese and bread" , "mouthful?" , "Cheesy snack" , "cheesy meal" , "Arbiter of tasty Welsh dish of cheese on toast" .)