Fruit essential to save delivery service (7)
I believe the answer is:
avocado
'fruit' is the definition.
(avocado is a kind of fruit)
'essential to save delivery service' is the wordplay.
'essential to' indicates the central letters.
'delivery service' becomes 'ocado' (Ocado is an online supermarket).
The centre of 'save' is 'av'.
'av'+'ocado'='AVOCADO'
(Other definitions for avocado that I've seen before include "Evergreen" , "Pear-shaped tropical fruit" , "Savoury pear-shaped fruit" , "Light green colour" , "Dull greenish colour" .)