Step? Those are the techniques my parents tried to use on me. It only made things worse. I dug in and refused to eat, no matter how hungry I got. When I started losing weight, Mom took me to the doctor so the doctor could talk sense into me. We came out with some sense alright... the doctor talked sense into Mom. Literally. If I was going to survive childhood, I was going to have to be accommodated.
Looking back? I had serious sensory issues that were never acknowledged, considered, or accommodated. Not ONE of them. Food only being one. I was so overloaded and overwhelmed 24/7 that... there was no way I could handle that kind of sensory challenge. Suicide looked better than that - and I was serious, but I never told anyone, and never acted on my plan.
I am similar. I have sensory issues with food that I have only realized they're sensory issues because of dealing with my child. I can't eat anything super soft, like squash (ugh, gross). I finally had zucchini bread because my daughter loves it and it wasn't too bad, I couldn't taste the zucchini. The items you're serving him, I wouldn't really touch. Fish, gross, sausage, gross because of the fat pieces. My meat needs to be cooked REALLY well (which is why he might like the bbq'ed meat). Yogurt has to have granola in it so I can chew it. I had weight issues in high school that could have been fixed if my parents actually helped me find things I liked other than the generic fat American food they were serving. I'm also a supertaster, I have more taste buds, so things like broccoli taste gross to me. But there are plenty of veggies I do like. And don't try sneaking things into my food. For one, I'll taste it, I'll FEEL it, and for two, I won't eat anything that I don't know what's totally in it, and I know if I'm lied to about food. I'd rather starve than eat something that I don't know what's in it (like a smoothie that is so blended I can't see what the ingredients are).
I was super picky as a kid, because my parents never listened to what I was saying. Now as an adult, my diet is vastly different that my parents. I have found a ton of things I DO like, but I live in an area that has a lot of great food. I have been able to introduce new foods to friend's kids when I've been told they won't eat veggies. I made it, didn't force them, and they eventually tried and liked it. My friend just didn't have enough of a variety of foods she served (as well as being a so-so cook, the type that thinks corn is a veggie and makes pasta, rice and corn for dinner).
A friend of mine has a child with Sensory Integration Disorder (SID) and her eating habits were horrible until her mom figured out it was all sensory.
Try something new, as somebody else suggested, things on pizza. Pesto, super fine veggies so they're easier to chew and they're more cooked. Let your child come up with a menu for the week. Find an ingredient that you know he does like, and find recipes that include that.