"just give them" doing a lot of work here.
Maybe I'm particularly bad at disguises or maybe my kid (just one, not the other) is Sherlock Holmes for food disguises, but this is nearly impossible for me. In that I can't generally find a way to do it.
Throw it into something they love. Sauces are a great way of hiding ingredients.
Problem is that it still looks like a sauce, which won't work for an anti-sauce hard-liner.
And he's remarkably astute detecting flavor variations.
No soups either, just raw ingredients? I would prepare his favorite food with minor variations, adding a little sauce or changing the texture, to broaden his horizons.
In your case, I would furthermore gamify it: I bet you can't figure out what I added or did differently!
I have one kid on which all this stuff would work.
And then I have the other kid. He will refuse to participate in the game. I keep the pressure on though. That means he's always exposed to foods outside the comfort zone without too much pressure. But efforts at subterfuge or psychology almost always backfire with him. So I keep all the cards on the table.
"This is a broccoli piece. You have to taste it or else {bribe}".
I don't have all the answers, but we've tried a lot of things with him.
Do keep in mind that sometimes things can be genuinely extremely unpalatable. There were common things I refused to eat as a kid because, well, it would literally make me puke.
If there's one thing on my 4 year olds plate that he "doesn't like", I have him close his eyes and try to guess which food item I just put in his mouth. After the game is over he'll usually just continue eating everything without complaint.