I would just put a fresh "salad" in his enclosure every day (the greens and veggies that AHBD mentioned are some of the very best ones to use) and let him eat as much as he wants all day -- he's not going to get fat on greens. Hopefully, he will eat more greens as he gets older (some beardies do, but they all have their own different preferences). You can take the leftover salad out when you turn off the lights at night and then put in a fresh one when you turn them back on the next morning. I put my beardie's salad in the corner at the cool end of his tank in a little "dish" (actually a plastic lid from a large jar of nuts -- turns out to be just about the right size and shape), with the greens floating in a little shallow puddle of water. That helps them stay fairly fresh for the whole day, and also helps him with
hydration if he ever decides to eat any (not very often in his case -- somewhere along the line my beardie decided he wanted to be a carnivore, but he still gets a salad every day just in case he changes his mind and decides to eat some.) :roll:
The "beautiful dragons" website that Jsw mentioned is one of the best sources of info out there (at least that I know of). You can print off the food list and take it to the grocery store with you to use as a reference.
If you can find some veggies that your little beardie likes, and if he can get into the habit of eating them regularly, count yourself lucky :wink: