K.H.
I really enjoyed being a mom except for the high chair and floor cleaning after meals. Spinach on the floor and high chair had me in tears one day, wishing that I was back in an office. That said, I can see how throwing the food on the floor could be really funny from a little boy perspective, especially if Mom has a huge reaction. Kids understand so much more than they can verbalize back. So I would tell him that he cannot have his plate anymore because he made a mess. And that when he practices keeping food on the tray, he can have more. Then let him have a very small portion. He may like having a spoon or even a kid size fork and a tiny cup with a ounce of liquid. Just give him a little bit at a time. He won't starve but he may fuss and be mad at the loss of his big game. Don't give a snack later unless he sits back in the high chair. You might want to eat off a cute kid plate and let him know that he can have one too if he learns to eat neatly.
Also, toddlers really enjoy cleaning up - sometimes too much and will make a mess just to clean it. But try giving him a wipe or a well-wrung sponge so he can pick up after himself. He could sweep crumbs into a dust pan too.
Good luck and have fun with him.