Place the pork pieces in a saucepan or dutch oven, add the tomato (cut in half), onion, garlic, salt and water. Bring to a boil, remove the impurities from it and lower the heat to low. Slow cook for 2 hrs.
Meanwhile drain the liquid that comes in the nopalitos, wash them through with clean water to remove some of the salt. Then place them in a bowl, add fresh water and set aside for 20 min. Then drain the water, cut them into little cubes
Check your pork after one hour and a half. Place the clean dried chillies and cook for 20 min. Then remove the chillies, tomato, onion and garlics and some of the liquid. Blend these ingredients very well until very smooth then pass the sauce through a sieve to get rid of any skins.
Then remove all the liquid left in the pork, leaving the meat by itself. Add the nopalitos and the sauce. Then if it the sauce needs more liquid, use the leftover. You want a thick runny consistency. Cook the pork, the nopalitos and the sauce (Chile Colorado) together for 10 min.