Become ready to eat pie prepared in service (5)
I believe the answer is:
ripen
'become ready to eat' is the definition.
(I've seen this before)
'pie prepared in service' is the wordplay.
'prepared' is an anagram indicator.
'in' means one lot of letters goes inside another.
'service' becomes 'RN' (abbreviation for Royal Navy).
'pie' is an anagram of 'ipe'.
'ipe' placed into 'rn' is 'RIPEN'.
(Other definitions for ripen that I've seen before include "Become ready for picking" , "Come to maturity like fruit" , "Mature, age" , "Develop fully" , "Become ready to harvest" .)