Very quickly, on the train, breaking the ice (2,1,5)
I believe the answer is:
in a trice
'very quickly' is the definition.
(I've seen this before)
'on the train breaking the ice' is the wordplay.
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'breaking' indicates anagramming the letters.
'train' with letters rearranged gives 'natri'.
'natri' put within 'ice' is 'IN A TRICE'.
(Other definitions for in a trice that I've seen before include "quickly" , "Pronto" .)