G.B.
Get a food chopper like the one Pampered Chef sells. Then put a serving of food on a cutting board. Then whack the top of the food chopper about 15 times. This will make all the food small enough he can eat it without chewing at all. Do each food separate so he gets the full taste of it. It's not puree or even blended. It's finely chopped.
As he ages he will learn more about the chewing.