– Place tomatoes and peeled garlic cloves in a saucepan, and cover with water. Cook over medium-high heat until tomatoes are soft, about 8 minutes.
– While the tomatoes are cooking, roast piquin peppers over a medium heat. Use a griddle or frying pan for this purpose, making sure you do not burn the peppers. It will take about 30 seconds to roast them. If you are not used to roasting peppers, turn the exhaust fan on. Set the peppers aside to cool.
– In a large frying pan, heat the oil, once it is hot, add the ground beef to cook. Stir occasionally to have an even cooking. After 5 minutes, stir in the chopped onion. Keep cooking.
– While the meat is cooking, place cooked tomatoes, garlic cloves, roasted piquin peppers, and 1 cup of the cooking water in your blender. Process until you have a smooth sauce.
– Pour sauce over the meat, and cook for 5 minutes. Add the nopales, and with your finger crush the dried oregano and stir in as well as the cilantro. Season with salt and pepper. Keep simmering for another 5 minutes to allow the flavors to blend, and the sauce has reduced a little.