my girl she's 2yo had the same prob with chewing.
i read on the web, realised is due to too much pureed food.
which is true enough, most of her food are pureed.
if any small chunks of meat, vege or even fish, she will spit out.
other than her porridge, she can chew any other food and snacks.
now we try to give her as much food in small pieces for her to chew.
like sweet corn with the comb, apple in whole and biscuits.
and she's somehow fussy or had a weird taste bud. she only eat simple things.
even carrot, eggs or tofu she dont like.
so far so good a little improvement.
and i will tell her chew these foods. so when feeding her porridge will keep telling her have to chew.
hope will be see more improvements.
not sure if this will help for your case.
my niece has shallow stomach and she have to eat smaller share and more meals each day.
but she's not fussy can chew and eat very well, she wasn't on too much pureed food not long after she starts on solids.