Church gathering incorporated piece of cake (5)
I believe the answer is:
cinch
'piece of cake' is the definition.
(both can mean something very easy)
'church gathering incorporated' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'gathering' indicates putting letters inside (gather can mean to acquire or bring in).
'incorporated' becomes 'inc'.
'ch' placed around 'inc' is 'CINCH'.
(Other definitions for cinch that I've seen before include "piece of cake" , "simple job" , "Doddle" , "In slang, a certainty or easy task" , "Something easily done" .)