Depends on the area and the cham, but during a dry season their meals would be small and infrequent - though most chams kept in captivity would have access to food year round and be able to snatch up any food that crossed their path (which would be regularly).
In the wild most larger chams will eat fledgling birds and small lizards/geckos and frogs, and would only need one of these every 4-5 days to really meet their metabolic demands.
As for the question of 'hunting' - no, hunting isn't really a priority. There's enough food where these chams live (common chams kept in captivity) that they could sit on one branch their entire life and enough food would come by that they could eat that they'd never have to move.
They are efficient hunters if anything, but they aren't cheetahs or peregrine falcons.