I'm not sure about chuckwallas, but I'm pretty sure most iguanas are almost exclusively herbivorous. Considering the effects of animal protein on green iguanas (liver and kidney disease), I would be very wary of feeding any animal protein to any iguana. You want dark leafy greens. NO LETTUCE. Lettuce has very little nutritional value, but the iguanas love it when you give it to them, and will eat little else. Tomato fruit is fine if the iguana even likes it, it depends on the individual, although some believe it's hard to digest. Tomato plant is toxic. Your iguana will let you know if it likes the tomato fruit or not. Grapes aren't toxic at all, and are routinely used to give the iguana medication. Fruits should make up less than 10% of the overall diet anyways. What you really want is dark, leafy greens, but no spinach. anapsid.org and greenigsociety.org/feedingigs.htm have an extensive list of which foods to feed, which foods not to feed, and which to feed in moderation. You should check it out, highest on the feed-list are dandelion greens, turnip greens, mustard greens, collard greens, watercress, stuff like that.