Rather weird headless fish on plate (6)
I believe the answer is:
oddish
'rather weird' is the definition.
(I know this)
'headless fish on plate' is the wordplay.
'headless' means to remove the first letter.
'fish' becomes 'cod' (type of fish).
'on' is a charade indicator (letters next to each other).
'plate' becomes 'dish' (type of plate).
'cod' with its first letter removed is 'od'.
'od'+'dish'='ODDISH'
(Other definitions for oddish that I've seen before include "Fairly unusual" , "A bit peculiar" , "Rather strange" , "kind of crackers" , "a little rum" .)