Toast the cascabel chiles on a preheated comal, or cast iron skillet, set over medium-low heat, flipping as they toast on all sides for a few minutes. Remove the stems and place them in a medium saucepan, cover with water and bring to a boil over medium-high heat, reduce to a simmer and cook for about 20 minutes, pushing them under water a few times as they cook, until fully rehydrated and softened.

Using a slotted spoon, transfer the chiles to the jar of a blender, along with 1½ cups of the cooking liquid, and puree until completely smooth. In a medium saucepan, heat 2 tablespoons of oil over medium heat. Once hot, pour in the pureed chile, add 1 teaspoon of salt, and let it cook and season for 5 minutes, stirring frequently, until darkened and thickened.

In a medium saucepan, bring salted water to a boil. Add the slice of the white onion, the whole garlic clove, and the nopalito strips, bring to a boil, then simmer for 7 to 8 minutes, until cooked through. Drain and set aside.

Season the meat with 2 teaspoons of the salt and the black pepper. In a large casserole, heat 3 tablespoons of oil over high heat. Once hot add the meat, and brown on both sides, for a few minutes. Add the crushed cumin and pressed garlic and stir. Once the meat juices have come out, add the chopped onion and cilantro, and cook for a few minutes. Pour in the seasoned, pureed cascabel chile along with chicken broth and remaining teaspoon of salt. Stir well and once it comes to a simmer, cover and reduce heat to medium low, and cook for 20 minutes. Incorporate the cooked nopalitos, stir well, and cook for another 20 minutes. Serve with warm corn tortillas and avocado slices.