... by eating citrus goodness (6)
I believe the answer is:
blimey
'by eating citrus goodness' is the definition.
I can't judge whether this definition defines the answer.
'by eating citrus' is the wordplay.
'eating' indicates putting letters inside.
'citrus' becomes 'lime' (lime is a kind of citrus).
'by' going around 'lime' is 'BLIMEY'.
Can you help me to learn more?
(Other definitions for blimey that I've seen before include "My word!" , "Surprised expression" , "well!" , "exclamation of surprise" , "Good gracious me!" .)