Bearded dragons can be trained. But I think for them other things are important (to most beardies) than for maybe most animals. My dragon for example won't come for an insect more than 1 - 2 of his body lengths away, despite his vision is for sure superb (he for example reacts to things going on outside of the window, or is very interested in watching me doing things) and directly for feeding time, of course he walks more than 1 - 2 body length. But an individual insect offered? Not worth it for him. So training him to come over when called as there is food would just not work. When called - my dragon recognizes his name, likely not as explicitly his name but as a sound I make before something interesting happens* - he looks, sometimes just with moving his eyes, whether there is something interesting, and then stays put. He's also not a dragon that runs to the glass once I approach or come home (some do) - he looks, and then he's fine with this like "I see my human is here, that's good!"
There exist studies in which bearded dragons are trained to open a door behind which there is an insect, then the behavior is filmed and other bearded dragons watching the movie are imitating it.
Also my dragon learned a lot of things, like that when he wants to come out, he has to go to an elevated place in his enclosure so I can get him out (enclosure opens from the top and is deeper than an armlength).
Also, he's learned a greeting behavior that is not a completely natural behavior: I pet his beard from the lip all the way down and only then he licks. Despite the licking is clearly one of his natural behaviors, the complete behavior, he's only doing so for greeting.
*He's always reacting to it. Despite I'm not always doing something special. I mention this regarding:
With food training you might teach yours to come when called but I suspect as soon as it figures out there isn't food every time it will stop coming on command.
So that I'm not always doing something (like: petting him, giving extra insects, taking him out) after saying "Taco!" doesn't make it less interesting for him.