IIRC, spring mixes often contain a lot of lettuces(?) Also not recommended, but only because some--like iceberg--have little/no nutritional value.
You can use the table
here as a guide.
I'm still having trouble finding stuff ZaRDoZ will eat. He seemed to nibble at turnip greens, but I haven't been able to find any locally in months. We put a new plant in his enclosure the other day (don't recall what--it was beardie safe, but not a "food" plant) and he chowed down on it. OTOH, there are a half dozen basil plants in there, and he ignores them. He does seem to like cilantro, and I use it to get him started on other greens. He's a challenge in most ways; I keep looking in the mirror, pointing to myself, and mumbling, "Smarter than lizards!"... but... :dontknow: