Like fillet? Be grateful for eating one (8)
I believe the answer is:
boneless
'like fillet?' is the definition.
(a meat fillet may be boneless)
'be grateful for eating one' is the wordplay.
'be grateful for' becomes 'bless' (bless can mean to celebrate or be thankful for).
'eating' is an insertion indicator.
'bless' going around 'one' is 'BONELESS'.
(Other definitions for boneless that I've seen before include "Filleted" , "lacking courage?" , "without skeleton?" .)