mealworms can cause impaction and should not be fed more than a treat once in awhile :/
Only if your lizard has other problems to begin with. Digesting exoskeleton is what chameleons do for a living. Lizard digestion in general is pretty amazing- my tegus and monitors digest chicken bones and beaks and feet, feathers, etc.
But mealworms are probably too high in fat to be a high percentage of the diet.
I feed a meal of mealworms about 1x per week and have done for years.
You want as wide a variety of feeders as possible. Mealworms are convenient and easy to grow, but there are better staples (crickets, roaches). Tropical roaches are very inexpensive and easy to breed. Dubia is a good choice.
In a laboratory setting, several generations of panther chameleon were successfully raised on alternating mealworms and crickets (see ferguson, panther chameleon). The percentage acceptable may be more than some here believe.
But it is still not the greatest idea in the world.
For single pet it shouldn't be expensive to alternate between a number of feeders- crickets, mealworms, superworms, waxworms, butterworms, soldier fly larvae, silkworms, roaches, etc.
Long term high percentage of mealworms is an experiment and risky with your lizard- bottom line.