Peel and dice the potatoes, about 1 inch in size.
Carefully transfer the potatoes into a sauce pan and cook in salted boiling water over medium heat. Don’t cook the potatoes all the way, we want them slightly under cooked and with a bite to them, (about 6-7 minutes). Remove from the heat, drain and run through cold water to stop the cooking process. Drain the water once again and set aside for later use.
Devein and toast the guajillos over low heat. Turn continuously to prevent them from burning (see notes below). Once fragrant and toasted on both sides, remove from the heat and rinse them. Place in a container and pour in hot water to rehydrate and soften them, (about 5 minutes).
Meanwhile, cook the chorizo over medium high heat in a large pan, (about 5-6 minutes). Remove from the pan and add the potatoes. Brown in the fat left behind by the chorizo (see notes below). During this time they will finish cooking. Right before the potatoes are done, lower to medium heat, add the diced onion and garlic, let them slightly soften. Incorporate the chorizo, mix everything well. Allow the chorizo to reheat. Remove from the heat.
Place the softened guajillos with the soaking water, garlic, oregano and salt into a blender. Process until everything is completely broken down and smooth. Strain if needed, pour in a bowl.
Heat a large pan, add 2 TBSP of olive oil. Place the closed bolillo bread in the sauce and coat the entire outside, top and bottom. If easier, you can brush it on. Then place the closed bread in the hot oil. Slightly fry the side touching the oil, about one minute. Turn so the other side does the same. Remove from the heat and repeat the same steps with the rest of the bread.
To serve, open the bread and place the chorizo with potatoes inside. Top it with the shredded ice berg lettuce, Mexican style cream, crumbled queso fresco and salsa. You could also add pickled jalapeños and avocado slices. Close the bread and enjoy!