Add the cactus to a small sauce pan, cover with water, add 1/2 teaspoon salt. Bring to a boil, reduce heat and continue cooking for 6 to 8 minutes; drain, rinse with cold water and set aside.

Add the tomato, tomatillo, chile de arbol, pinch of salt and 1/4 cup of water to the blender. Blend on high until smooth, set aside. Add a little more water if needed.

In a medium skillet, preheat oil to medium heat for a few minutes. Add the onions and serrano chile, cook for 2 minutes.

Add the salsa from the blender and bring to a simmer, cook for 2 to 3 minutes, taste for salt. Add the cactus and cheese slices and continue to simmer for another 2 minutes. Serve with warm corn tortillas or Mexican bolillo rolls.

Garnish with cilantro and avocado slices.