Round about lunchtime, set to have food (6)
I believe the answer is:
'food' is the definition.
(plaice is a kind of food)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for plaice that I've seen before include "Flatfish, valued as food" , "The fish sounds as if it hits the spot" , "Swimmer" , "Important food fish" , "Location of the fish" .)