Make a lengthwise cut on 1 side of the guajillo chiles and remove seeds. Put chiles in a bowl and cover with boiling water, letting soak for 20 minutes or until soft. Place chiles and some of the soaking water in a blender, puree with garlic and onion, strain and set aside.
Cook the potatoes whole with skin on in salted water for about 25 minutes or until they feel soft. Then remove the skin and cut into small dice.
In a medium-size non-stick skillet cook the chorizo at low heat and remove all the excess oil, add the diced potatoes and mix; season with salt.
Stuff the bread with the potato-chorizo mixture. Dip the stuffed bread in the guajillo sauce and saute in the hot oil on both sides.
Right before serving mix the cabbage with the vinegar, divide and insert into the sandwich.