Smugglers left to finish one's healthy breakfast (6)
I believe the answer is:
muesli
This clue could be a double definition.
'smugglers left to finish one's healthy' is the first definition.
I know that 'healthy' relates to this answer.
'breakfast' is the second definition.
(common breakfast food)
(Other definitions for muesli that I've seen before include "Dish of dried fruit and cereals" , "Mixture of crushed grain, nuts etc" , "eaten at breakfast" , "Mixture of crushed cereals. nuts and fruit" , "Breakfast mixture of dry cereals and fruits" .)