In the wild they eat primarily insects but also take occasional green leafy vegetable matter and flowers. I would be a bit cautious about offering fruit as it is high in fruit sugar (fructose) which is different from the nectar found in flowers. My favourite edible plant to recommendation for lizards is dandelions - they love the yellow flowers and the leaves are high in calcium. Nasturtiums are another edible flower and leaf, with the leaves being high in vitamins A, C and D. These can both be easily grown from seed in pots (or purchased from a garden outlet) and whole plants put in with the lizards to decimate at their leisure.
Hibiscus flowers are also relished by many lizard species. In terms of leaf greens, the following would be suitable for netted dragons… kale, beet greens, mustard greens, broccoli greens, turnip greens, bok choy, pak choy, parsley, clover, cabbage. Given that the lizards will not be tearing appropriate sized mouthfuls off the plant, as they would in nature, it is very important that you chop the leaves into bite sized pieces before offering them. An appropriate size is about half as big as the head or as wide as the distance between the eyes.