When you say lizard, I guess you mean a salamander or something along those lines(unless you live in the Southwest). No, it's not good for the cats digestion and may give it the runs, but it's like eating a bird or a mouse. The real danger from those two are transferable diseases and bones getting stuck in digetive tract,=. But most lizards do not have hard skektons, especially aquatic type. Just watch cat for next 24 hours. If it really is disagreable to the cat, it could throw it back up if it can't digest it.
I live in southern Mississippi and we have little grey or green lizards. My cat eats them all the time. He also eats mice, rats, toads, baby bunnies, and birds. I've never had any problems with his diet... Except when he decides to bring them inside the house.
Our veterinarian said lizards are not bad for cats to eat; but baby rabbits will make them sick.
I would contact a vet as a lot of amphibians and reptile can be venomous. Even if not venomous they can make your cat a bit under the weather for a while, either way contact your vet ASAP.
It depends on whether it was your pet lizard. Lizards are pretty tasty.
Instinct and/or trial-and-error will inform the cat about what is and is not good to eat.
Only if it is a Gila monster or a beaded lizard, both of which are poisonous, and warn of this with their black and yellow colouring.