I'm off toast! (7)
I believe the answer is:
cheerio
'toast' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for cheerio that I've seen before include "A hearty farewell, begins with applause" , "Bye" , "See you" , "British romance imprint" , "Expression used when leaving" .)