K.T.
Not to sound mean, but it sounds like the two of you have some personality issues rather than eating issues. It sounds like his solution of "holding foods in his mouth" is a protest to your requests, demands, tone of voice, rules, threats, and punishments. Think of it this way, if he takes the food off the plate, then he does what you want "clear the plate" but he is "thumbing his nose at you" by refusing to swallow it. Which is his way of saying "I'm not going to go along with your rules, but you are my mom, and I don't want to totally disrespect you."
I may be way off, and if I am, my apologies if I sound like I am psychoanalyzing.
I sounds like he doesn't want to make you mad, but wants something other than what is happening.
He may want to eat different food. He may want to be treated differently.
Just my 2 cents. I have a son who is 3 1/2 and we eat pasta and pizza more than I care too, but he eats a lot of healthy choices with snacks so I know he well nourished. I really really think the psychology associated with eating foods is as important if not more important than how balanced the meal is, because mental & emotional associations condition how much you eat and why you eat and even what you choose to eat. Think depressed lonely person who eats a lot of sugary food to make themselves feel more sweetly loved.
AS a mom, we train kids how to use the potty and we also need to train them how to like food and the right kinds of foods.
Stay positive and both of you try to be happy with food! It's the Earth's bounty after all and we need to be thankful for what we have. Even if it's a dinner of popcorn and apple slices, it's still very good for you. He'll learn, but stay positive and teach him how to be happy with foods too.
Best wishes,
K.
(PS I love food, can you tell!)