Mine eat most things in the fridge, chopped broccoli, spinach, grated carrot, grated apple, fresh corn chopped, grated zucchini, celery leaves, grated pear, chopped kiwi fruit, chopped strawberries.
They barely touched any of it until nearly 12months old, now they love a good salad
Mix a bit if calcium supplement with it.
As for crickets, I've always just dumped a stack in there, the dragons will gobble a heap straight away, then pick off the ones that managed to hide quick enough later.
Try to vary the insects you feed them too. I use wood roaches (bred in a colony at home) meal worms, earth worms, caterpillars, spiders, moths, blowflies etc. I catch insects about the house, but we live in a bushy area and don't use chemicals in the house or garden.