Slam in the lamb, perhaps (5)

I believe the answer is:

roast

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'slam' is the definition.
(both can mean to heavily criticise)

I can't explain the remainder of the clue.

(Other definitions for roast that I've seen before include "Cooked meat; criticise" , "Sunday tradition" , "Pull to pieces" , "Sunday meal" , "Oven-cook, tease" .)

I've seen this clue in The Guardian.

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