I guess it depends on how old your cham is
I am going to quote this right from the "Chameleons in Captivity" book by Connie Dorval
"Insects should be coated with supplement before being offered to the cham. Female and juveniles should have their insects coated every feeding, while adult males require a third less, therefore coat the insects 4 to five days a week."
"Vitamin supplement should be used once a week"
I took this from page 24 and 25 of the diet chapter.
Personally, I give my chams a varied diet of Dubias, phenix worms, crickets along with putting them outside twice a week.
I dust the babies every day and the adults like every couple of days. They are healthy and growing pretty fast...
Hope that helps.