Wonderful evening meal: one starter of prawns less (5)
I believe the answer is:
super
'wonderful' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
(Other definitions for super that I've seen before include "Prefix meaning above or informally great" , "First-rate, top-notch" , "Excellent; policeman" , "Top" , "Delightful" .)