How does he get food into his mouth? (daft question but vital info!) and does he chew it?
I suggest, Create delay/ slow-down tactics. Less eating with hands.
Teach him to handle / eat with very small child sized cutlery, one implement in each hand "like a grownup" and teach him how to hold down a potato , carrot, brocolli etc with the fork and cut it up with his knife, use fork or small spoon to transfer it to mouth. This will naturally slow down his eating.
If he would like a slice of cake, let him cut it from the cake, transfer to his own plate, cut it up and eat with his knife and fork..
Let him butter his own slice of toast/butter and fill his own sandwich/, then decide how many little sandwiches you can help him cut it into.
Cereal; offer shreddies or some other small- bite sized cereal .
Let him slice up a banana/apple and eat one slice at a time.
Eat together at the table and encourage conversation while eating, to slow down the mouthfuls.
Although cutting everything up tiny tiny is tempting, giving him larger pieces of food which then have to be chewed, might work better.