A hit lyric that's fashionable (1,2,4)
I believe the answer is:
a la mode
'fashionable' is the definition.
(a la mode can mean trendy or fashionable)
'a hit lyric' is the wordplay.
'hit' becomes 'lam' (to 'lam' means to hit hard).
'lyric' becomes 'ode' (ode is a kind of lyric).
'that's' acts as a link.
(Other definitions for a la mode that I've seen before include "In the fashion, in Paris?" , "Fashionable -- served with ice cream" , "stewed with veg?" , "In the current fashion" , "Do a meal in French style (1, 2, 4)" .)