easiest way to peel/skin a tongue?
You'll need a lot longer than 20 minutes that the recipe suggests.  For cow tongue, we usually let them sit in a crock-pot for about 4hrs.  My guess for lamb tongue is about 90 minutes on low simmer.

The skin tends come loose from the muscle underneath when done. The best trick I've found is to cut the skin down the center of the tongue (lengthwise). Use a sharp knife and try not to cut too much of the muscle or some of the meat will peel with the skin.  

You can then peel off the skin easily ending up in two sheets (one for each side). Wearing latex or dishwashing gloves helps buffer some of the heat, but as long as they are above room temperature the peeling should go fine and easy.