Toast secures treat successfully in collapsing hot-dog (4,6)
I believe the answer is:
good health
'toast' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'treat successfully in collapsing hot-dog' is the wordplay.
'treat successfully' becomes 'heal' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'collapsing' indicates an anagram.
'hot'+'dog'='hotdog'
'hotdog' anagrammed gives 'goodth'.
'heal' inserted within 'goodth' is 'GOOD HEALTH'.
'secures' is the link.
Can you help me to learn more?
(Another definition for good health that I've seen is " Cheers!".)