Every Cham is different. It may not accept a new food at first or it may go crazy as if it's never eaten before.
Every cham I've ever had has accepted all food items without reservation. I would start with Silkworms however. Chams love 'em. For my 2 chams, the first food I offered both of them were silkworms. Immediately after the most stressful time of their lives (being shipped from Cali to Michigan), I offered silkworms several hours after they were introduced into their cage and they ate the worms within minutes.