While you need to know that there is no reason why your chameleon is not growing (such as parasites, etc.) it also is not necessarily a good thing to grow them too fast in captivity IMHO because it's hard to ensure that your supplementing, etc is sufficient to keep up with the bone/body growth.
You can feed it at that age as much as it will eat in a couple of minutes at each feeding.
You can use a wide assortment of greens such as collards, escarole, endive, dandelion greens, kale, endive, mustard greens, etc and veggies such as carrots, sweet red pepper, squash, zucchini, sweet potato, etc. For gut loading/feeding the insects such as crickets, roaches, locusts, superworms.
Generally supplementing should be phosphorous - free calcium powder at most feedings, phosphorous free calcium / D3 powder twice a month and a vitamin powder that contains a beta carotene (prOformed) source of vitamin A twice a month.
Whatbuvb light do you use and how old is it? What are the basking temperatures?
