Performing well in lessons on green (2,4)
I believe the answer is:
on song
'performing well' is the definition.
(I've seen this before)
'in lessons on green' is the wordplay.
'in' indicates a hidden word.
'ON SONG' is hidden in the letters of 'lessons on green'.
(Other definitions for on song that I've seen before include "Performing well (colloq.)" , "Vocally" , "In superlative form" , "in fine form" , "on top form?" .)