Extra protection on helmet gets one almost cooked (6)
I believe the answer is:
'extra protection on helmet' is the definition.
(grille can mean a bar on a helmet visor)
'one almost cooked' is the wordplay.
'one almost' means to remove the last letter (most of the word but not all of it).
'cooked' becomes 'grilled' (grilling is a kind of cooking).
'grilled' with its last letter removed is 'GRILLE'.
'gets' acts as a link.
(Other definitions for grille that I've seen before include "Protective lattice" , "Frame of bars" , "Metal lattice-work" , "Part of an air-cooling system" , "Metal lattice" .)