Papa I caught with mainly pleasant piece of cake (6)
I believe the answer is:
picnic
'piece of cake' is the definition.
(both can mean something easy)
'papa i caught with mainly pleasant' is the wordplay.
'papa' becomes 'P' (phonetic alphabet: alpha, bravo, charlie etc.).
'caught' becomes 'c' (cricket abbreviation).
'with' is a charade indicator (letters next to each other).
'mainly' means to remove the last letter (virtually or mainly the word, but not all of it).
'pleasant' becomes 'nice' (similar in meaning).
'nice' with its last letter taken off is 'nic'.
'p'+'i'+'c'+'nic'='PICNIC'
(Other definitions for picnic that I've seen before include "Alfresco meal" , "outing" , "outdoor eating" , "Alfresco repast" , "food for consumption outside" .)