They serve a nice portion during meals (7)

I believe the answer is:

menials

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'they serve a nice' is the definition.
The definition suggests an adverb but the answer is not.

'portion during meals' is the wordplay.
'portion' becomes 'ni' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'during' indicates putting letters inside.
'ni' put inside 'meals' is 'MENIALS'.

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I've seen this clue in the Evening Standard.

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