I believe Romain is fine but regular lettuce has no nutritional value. That said there are much better choices, such as collards, mustard greens, etc... Chameleons are insectivores so they also need their bugs to thrive.
You can offer your chameleon slices of apple, pear, berries, melon...but not too much fruit. You can offer it kale, dandelion greens, thin slices of sweet potato, zucchini, sweet red pepper, etc.
All of these things can also be used to feed/gutload superworms, crickets, locusts, roaches. You want healthy insects to feed to your chameleon.