Norma is not such easy work (5,5)
I believe the answer is:
light opera
'norma is not' is the definition.
I can't tell whether this definition defines the answer.
'easy work' is the wordplay.
'easy' becomes 'light' (similar in meaning).
'work' becomes 'opera' (musical work).
'light'+'opera'='LIGHT OPERA'
'such' acts as a link.
Can you help me to learn more?
(Other definitions for light opera that I've seen before include "musical entertainment" , "'The Mikado', e.g." .)