I don't think their sap is toxic at all, so I dont think you have anything to worry about there...
I say don't boil them at all because by boiling them, you are leeching out all the nutrients that make them good for your lizard. I would just make sure you know that they havent had weed killer put on or near them. If its your garden, then you will know this (i hope!)
My budgie loves dandelions, and my neighbours love giving them to me! gets them out of the garden!