Food fan: I'm tucking into split (9)
I believe the answer is:
nutriment
'food' is the definition.
(nutriment is a kind of food)
'fan i'm tucking into split' is the wordplay.
'fan' becomes 'nut' (I've seen this before).
'tucking into' means one lot of letters goes inside another.
'split' becomes 'rent' ('rent' can be a synonym of 'split'**).
'im' placed within 'rent' is 'riment'.
'nut'+'riment'='NUTRIMENT'
(Other definitions for nutriment that I've seen before include "diet" , "It sustains" , "Sustenance, nourishment" , "Nourishing food" , "Material providing food" .)