Rascal gets one form of seafood (6)
I believe the answer is:
scampi
'form of seafood' is the definition.
'scampi' can be an answer for 'seafood' (type of seafood). I'm not certain of the 'form of' bit.
'rascal gets one' is the wordplay.
'rascal' becomes 'scamp' (synonyms).
'gets' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'scamp'+'i'='SCAMPI'
Can you help me to learn more?
(Other definitions for scampi that I've seen before include "Large sauteed prawns" , "Cooked Norway lobsters" , "Large prawns cooked in batter" , "Cooked Norway lobster" , "Dish of deep-friend prawns" .)