Scallywag at lunchtime has seafood (6)
I believe the answer is:
scampi
'seafood' is the definition.
(type of seafood)
'scallywag at lunchtime' is the wordplay.
'scallywag' becomes 'scamp' (synonyms).
'at' is a charade indicator (letters next to each other).
'lunchtime' becomes 'I' (one o'clock is I on a clock with Roman numerals).
'scamp'+'i'='SCAMPI'
'has' is the link.
(Other definitions for scampi that I've seen before include "Large prawns cooked in batter" , "Breaded prawns" , "Prawns (fried with breadcrumbs)" , "Tasty prawns in batter" , "Dish of fried shrimps or prawns" .)