Begin eating, adding occasionally one starter from Nando's (3,2)
I believe the answer is:
dig in
'begin eating' is the definition.
(I've seen this before)
'adding occasionally one starter from nando's' is the wordplay.
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
'one' becomes 'i' (Roman numeral).
'starter from' says to take the initial letters.
The first letter of 'nando' is 'n'.
The alternating letters of 'adding' are 'dig'.
'dig'+'i'+'n'='DIG IN'
(Other definitions for dig in that I've seen before include "Begin eating heartily" , "Enjoy the food" , "Start to eat" , "protect himself" , "Start to scoff" .)