Lad, go on overturned boat (7)
I believe the answer is:
Here is my best explanation:
'boat' is the definition.
(gondola is a kind of boat)
'lad go on overturned' is the subsidiary indication.
'overturned' is an anagram indicator.
'ladgoon' with letters rearranged gives 'gondola'.
(Other definitions for gondola that I've seen before include "water transport", "Shop unit", "Supermarket display unit", "Traditional rowboat of Venice", "Venetian canal boat", "Venetian taxi", "mountain climber", "Goon lad (anag.)", "Venetian boat - airship cabin" and "In canal boat".)