Annoyed worker eating one roll for breakfast (9)
I believe the answer is:
'roll for breakfast' is the definition.
(a croissant might be eaten for breakfast)
'annoyed worker eating one' is the wordplay.
'annoyed' becomes 'cross' (cross can mean angry).
'worker' becomes 'ant' (worker is a type of ant).
'eating' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'crossant' placed around 'i' is 'CROISSANT'.
(Other definitions for croissant that I've seen before include "Tasty crescent-shaped French bread roll" , "French breakfast food" , "A rich crescrent-shaped bread roll" , "French pastry" , "Breakfast pastry" .)