Make the guajillo salsa. Add the guajillo chiles and enough water to cover them completely to a small saucepan or pot. Bring to a boil over high heat. Remove the pot from the heat, cover, and let the chiles soak for 10 minutes to soften.
Using a slotted spoon, transfer the softened chiles to a blender. Add the chipotle peppers, tomato, garlic, salt, and oregano. Blend until smooth. Pour it into a small bowl and set aside.
Cook the nopales. Add the nopales, 1 teaspoon of kosher salt, and enough water to cover them completely to a medium saucepan or pot. Bring to a boil over high heat, reduce the heat to low, cover, and simmer for 10 minutes.
Drain the water from the nopales and give them another rinse under warm water to remove any excess slimy liquid.
Heat the olive oil in a large skillet over medium-high heat. Add the onion and bell pepper, and sauté for 6-7 minutes until soft and translucent.
Add the cooked nopales, the remaining 1 teaspoon of kosher salt, garlic powder, onion powder, ancho chili powder, and black pepper. Cook for an additional 3-4 minutes to meld the flavors.
Serve the nopales filling in warm corn or flour tortillas with a spoonful of guajillo salsa and a pinch of crumbled queso fresco.
Notes
Preparing the nopales. You can usually buy cactus paddles already cleaned with the spines and thorns removed, sometimes even sliced. If yours still have thorns, here's how to clean and prepare nopales first. Four large paddles come out to roughly 3 to 4 cups once they're sliced.
Jarred or canned nopales. These work too, just drain and rinse them well. Skip anything labeled en escabeche or pickled, since they're packed in vinegar.
Chili powder. I use ancho chili powder, but regular chili powder or chipotle powder works just as well.
To store. Refrigerate the nopales filling in an airtight container for up to 3 days. Keep the guajillo salsa in its own container for up to a week.
To reheat. Microwave the filling for 1 to 2 minutes, or warm it in a skillet over medium heat until heated through.