I never really did understand the picky eater concept. No offense to anyone, but in all the instances I've witnessed, it's mostly due to parents catering to the child.
My kids always just ate everything. They knew I wouldn't give them anything gross or anything that I wouldn't eat myself. In fact, my son is a very adventurous eater. He eats things I would never eat, like chicken hearts, gizzards. He will literally try anything. My daughter did go on a brocolli strike once after finding a green worm on her cooked brocolli, but it didn't last that long because it's one of her favorite foods.
As moms, it makes US feel better when our kids eat something. It's completely natural. However, kids will eat anything if they get hungry enough. Or at least be willing to take a taste.
It's my very strong opinion that kids who won't eat healthy things that get prepared for them should have zero access to things like pop-tarts, chips, sugar cereals, cookies, etc. Kids don't need sugar. They DO need nutritious foods.
From the time my kids were very, very little, when I went grocery shopping, the first area we went to was the produce section. I told my kids they could choose anything in the entire section and I'd buy it for them. The only deal was.....they had to be willing to taste it. The produce section is a wonderful place to learn about colors, different textures, aromas...and that's before you even get the stuff home. They got to make their choice which got that out of the way. They didn't get to ask me for other things throughout the store. It's a habit I got my kids into, it worked pretty great, and they were much more willing to taste things that they had picked for themselves. As a result, my kids tried, and liked, a huge variety of fresh produce. One time, a man approached me and said, "Excuse me....did I just hear your little kid begging you for eggplant?" Yep.
I think the key is in exposing kids to a variety of things. How can they know they don't "like" something if they've never tried it? The answer is that they can't. My kids certainly went through phases of being hooked on certain things. They might go on a mango or brussel sprout kick. Fine with me. They didn't eat that INSTEAD of anything else.
Your son is 5. Get him involved in helping you pick things out and prepare them. You know he likes chicken. How about having him help you bake one? He likes potatoes. Give him a masher and let him help you make mashed potatoes. Expand on his horizons a little.
I agree with not making it a battle. He can eat what you make or not. That's giving him a choice.
My mom made bizarre things for dinner sometimes like scrambled eggs and oysters. I just brushed my teeth, put my nightgown on and kissed everyone goodnight because I knew I was going to bed with no dinner if I wouldn't eat it. My choice. Better luck tomorrow.
Get rid of the sugar, tweek the things he likes, and let go of thinking that ANYTHING he will ingest is better than nothing at all.
Just my opinion.