Blast top of orange to get zest (5)
I believe the answer is:
gusto
'zest' is the definition.
('gusto' can be a synonym of 'zest')
'blast top of orange' is the wordplay.
'blast' becomes 'gust' ('gust' can be a synonym of 'blast'**).
'top of' indicates taking the first letters.
The first letter of 'orange' is 'o'.
'gust'+'o'='GUSTO'
'to get' acts as a link.
(Other definitions for gusto that I've seen before include "Verve, zest" , "Obvious enthusiasm" , "Vigorous and enthusiastic enjoyment" , "Great enjoyment, vigour" , "Showing zest" .)