Place the clean nopales inside a pot with nothing in it! no water, no oil, just the pot with the nopales inside.
Cover the pot with a lead and let the nopalitos cook at medium heat.
Nopales have the slime and a lot of water and they literally cook in their own juice.
cook the nopales at medium heat for 20 minutes or until they all have changed to an olive green color and feel soft.
Place the nopales inside a strainer and rinse with cold water, this will stop the heat and will help you to get rid of the slime that they could still have.