Knight turns up with extravagant oval dish (7)
I believe the answer is:
risotto
'dish' is the definition.
(risotto is a kind of dish)
'knight turns up with extravagant oval' is the wordplay.
'knight' becomes 'sir' (a knight has the title Sir).
'turns up' shows that the letters should be reversed in order.
'with' says to put letters next to each other.
'extravagant' becomes 'OTT' (abbreviation for 'over the top').
'oval' becomes 'O'.
'sir' reversed gives 'ris'.
'ris'+'ott'+'o'='RISOTTO'
(Other definitions for risotto that I've seen before include "Perhaps Italian" , "Main course" , "You cook it in stock" , "dishy thing!" , "F" .)