Salad plant to reveal unexpectedly to big cat, first off (6,5)
I believe the answer is:
spring onion
'salad plant' is the definition.
(I've seen this before)
'reveal unexpectedly to big cat first off' is the wordplay.
'reveal unexpectedly' becomes 'springon' (to spring something on someone).
'to big cat' becomes 'lion' (lion is a kind of big cat).
'first off' means to remove the first letter.
'lion' with its initial letter removed is 'ion'.
'springon'+'ion'='SPRING ONION'
'to' acts as a link.
(Other definitions for spring onion that I've seen before include "Bulb with leaves eaten in salads" , "Salad plant" , "Salad vegetable" , "one of the greens" , "salad ingredient" .)