Lukewarm food served up, including pathetic starter (5)
I believe the answer is:
tepid
'lukewarm' is the definition.
(I know that lukewarm can be written as tepid)
'food served up including pathetic starter' is the wordplay.
'food' becomes 'diet' (diet is a kind of food).
'served up' is a reversal indicator (in a down clue, letters go up).
'including' means one lot of letters goes inside another.
'starter' says to take the initial letters.
The first letter of 'pathetic' is 'p'.
'diet' written backwards gives 'teid'.
'teid' enclosing 'p' is 'TEPID'.
(Other definitions for tepid that I've seen before include "Slightly warm" , "without passion" , "lacking enthusiasm" , "without enthusiasm" , "Unenthusiastic - cool" .)