K.A.
Don't let him choose an alternative to what you have already fixed for a meal. He can eat it or go hungry. Save his plate and when he comes back and says he is hungry give it back to him. He will eat when he is hungry. If you continue to give him an alternative meal, he will continue it throughout his life. Besides, you know what is good for him and what is not. He should not be allow to choose something that is not good for him over the health meal on the table. I fix my kids plates and I put on it what I want them to eat in the amounts I think they are capable of eating. Seconds are allowed but only after you have cleaned your plate the first time. I have a rule in my house that you have to eat the fruit and vegetables on your plate before you leave the table. I don't care if you don't like it, eat it anyway. We did have some gagging and throwing up when I first made the rule, but now they just eat them and don't fuss. I am not such a sticker on the rest of the food on their plate, but they are not getting an alternative. If they come back hungry, they can finish their plate. If they did finish their plate then we can talk about a snack.
My MIL used to fix my husband alternative meals when he did not like what she fixed. After we got married he tried that on me. NO WAY!!! We are on a very tight budget and I can't afford to fix 2 meals to make you happy. You will learn to eat what is on the table. If I fix something you don't like, let me know and I will try not to fix it again. If you like something I fix, let me know so I can fix it in the future. But if it is on the table already, you will eat it or starve. My MIL still does this for my SIL who is 38. They can afford it, I can't.