You need to be patient. Let your animal get comfortable feeding without you watching. It also may be nocturnal and not want to eat during the times you are trying to feed/watch.
Some people like the nutrition found in them. Avocados have fatty acids and other nutrients, and they don’t have as much calories as butter when you are baking. Other people...
Iguanas, bearded dragons, uromastyx lizards and some skinks are omnivorous, hence they'll be able to feed on either. Other lizards are strict carnivores, mostly feeding on small invertebrates.
You could start training him now by getting him accustomed to having weight on his back, basically turning him into a pack-steer. But, he won't be ready to actually ride...