Oh my gosh-
Mealworms do have nutritional value you guys, and it can be signficant, especially when they are fed a good diet and not bran. Scan my back posts for more info- too lazy to post same stuff again and again and too lazy to keep references handy. But somewhere in there in the past year or two you can find links to nutritional analysis of mealworms that found they are comparible to crickets in some ways and superworms in others.
Yes- use as part of a varied diet. But there is no need to eliminate them, and they do provide benefit as variety. I breed zillions and feed them about 1x per week as an entire feeding to the lizards. I feed them the same dry stuff I feed other insects like crickets and roaches- the same good stuff goes into them. Just less fresh veggies and fruit, but even that goes into them as well.
Ferguson, in his panther chameleons book, reported that he used mealworms and crickets only (those two insects only) to breed multiple generations of panther chameleons in his lab. Furthermore, he reported that laboratory analysis of crickets and mealworms fed the same diet, found that the mealworms had a higher calcium content than the crickets fed the same diet. Which is one reason he included them in his chameleons' diet.
If mealworms had no nutritional content, leopard gecko breeders would not have been able to use them over many generations as a single food source for their animals, and they would not have geckos living in excess of 20 years on such a diet.
OP- for a single meal, just feed as many as your lizard wants for that meal. Use appropriately sized mealworms for your animal- tiny worms for baby chameleons. And use for variety only- not as the primary food source. Use as many insects as you can for variety.