Free lunch lacking core ingredient turned out to be pleasant (8)
I believe the answer is:
cheerful
'pleasant' is the definition.
(similar in meaning)
'free lunch lacking core ingredient turned out' is the wordplay.
'lacking core ingredient' suggests removing the centre (the core of the word is removed).
'turned out' is an anagram indicator (turn out can mean to organise).
'lunch' with its middle taken out is 'luch'.
'free'+'luch'='freeluch'
'freeluch' anagrammed gives 'CHEERFUL'.
'to be' acts as a link.
(Other definitions for cheerful that I've seen before include "Happy and optimistic" , "Optimistic and upbeat" , "In a happy mood" , "gay" , "Lure chef into being in good spirits" .)