Mutual friend eating fabulous bird with cooked rice (10)
I believe the answer is:
reciprocal
'mutual' is the definition.
(I know that mutual can be written as reciprocal)
'friend eating fabulous bird with cooked rice' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'eating' is an insertion indicator.
'fabulous bird' becomes 'roc' (mythical or fabulous giant bird).
'with' says to put letters next to each other.
'cooked' is an anagram indicator (letters cooked into a new form).
'pal' enclosing 'roc' is 'procal'.
'rice' with letters rearranged gives 'reci'.
'procal' put after 'reci' is 'RECIPROCAL'.
(Other definitions for reciprocal that I've seen before include "Cross" , "with give and take" , "Mutual" , "Done in return" .)