Mention of first person, one topping the order? That's a surprise! (3-6)
I believe the answer is:
eye-opener
'a surprise' is the definition.
(eye opener is a kind of surprise)
'mention of first person one topping the order?' is the wordplay.
'mention of' indicates a 'sounds like' (homophone) clue (I've seen 'mentioned' mean this).
'first person' becomes 'I' (first-person pronoun).
'one topping' is a charade indicator (letters next to each other).
'the order?' becomes 'opener' (I can't justify this - if you can you should give a lot more credence to this answer).
'i' sounds like 'eye'.
'eye'+'opener'='EYE-OPENER'
'that's' is the link.
Can you help me to learn more?
(Other definitions for eye-opener that I've seen before include "Fact that brings great surprise, dilating optics" , "This surprises greatly - makes you look" , "Something startling" , "Surprise revelation" , "Fact that brings great surprise - wakes you up" .)