Three year olds are at a wacky point where there really is such a thing as too much of a choice. It's like the part of their brains that are developing the sense that there is a whole other path leading from the alternate decision causes them to stop and freeze when it comes to the crossroads, and many times, the decision part is overwhelming. While it's awesome to help them develop the ability to serve themselves, it can also temporarily be wayyyy too much, and honestly, instead of standing there and trying to play the wheel and deal game in the effort to get him to jump ahead of his developmental area and "think of others" and not take so much, I would simply alter dinner time so that you serve plates, and later if he wants more, he can grab a spoon and help himself, if you are so inclined. It's asking much too FAR too much to try to rope a three year old into being that kind of decision maker.
Kind of like, asking a student of arithmetic to instantly do a page of geometry with correct solutions. They have the tools, a bit, but not enough of them, and not in a way that they can make heads or tails of the Geo problems.
I have ideas for other things, too (my two are two years and nine months apart) but I'm waiting a sec, because your phrasing of "totally useless to fix and have tantrums over" is stopping me a bit. Tell me about your thoughts on tantrums. Do you want him to not tantrum, or to avoid tantrums?