We had the same problem here too - though come to think of it, DS hasn't been quite as bad with chucking food recently. We have always just ignored him throwing the food on the ground - we didn't want to draw attention to it and make it into a game!
Like others have said, DS usually chucked food when he was getting full. Sometimes he just seems to do it when he has a lot in front of him. One thing that I noticed helps is giving him small bits of the food at a time. So, instead of giving him a full bowl/plate of say meat and vegetables, we might give him a piece of carrot, then hand him a bit of potato, etc. If he's in a chucking mood we usually resort to this.

HTH Good luck, I know how frustrating it is!