Dish with mashed pea all served up (6)
I believe the answer is:
paella
'dish' is the definition.
(type of meal)
'mashed pea all served up' is the wordplay.
'mashed' is an anagram indicator.
'served up' says the letters should be written backwards (in a down clue, going upwards).
'all' reversed gives 'lla'.
'pea' is an anagram of 'pae'.
'pae'+'lla'='PAELLA'
'with' is the link.
(Other definitions for paella that I've seen before include "Spanish course" , "Spanish dish based on saffron rice" , "Spanish dish of rice, meat and seafood" , "Fare for Spaniard" , "Spanish dish of rice, saffron etc." .)