Rascal at lunchtime has seafood (6)
I believe the answer is:
scampi
'seafood' is the definition.
(type of seafood)
'rascal at lunchtime' is the wordplay.
'rascal' becomes 'scamp' (synonyms).
'at' says to put letters next to each other.
'lunchtime' becomes 'I' (one o'clock is I on a clock with Roman numerals).
'scamp'+'i'='SCAMPI'
'has' acts as a link.
(Other definitions for scampi that I've seen before include "sort of seafood" , "Cooked Norway lobsters" , "Large prawns as food" , "Dish of cooked shrimps or prawns" , "Cooked Norway lobster" .)