Veggies are important, especially as the dragon gets older. If he is only 6" long then it is likely he is still quite young. Offer greens daily, feed him crickets or other suitable insects (ie silkworms, roaches, butterworms) twice a day till he is about 6 months, then drop insects to only once a day.
Best way to get them to eat their veggies is to cut them very fine, put a bit into a dish then add crickets (or other insects as indicated above). As he goes for the insects, he will inadvertantly take some greens and get a taste for them. Always use a mixed variety of greens, such as collard greens, dandelion greens (and flowers), endive, escaroli, turnup greens, mustard greens and other dark leafy greens high in calcium and other nutrients.
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PHLdyPayne