Preparation

Make the guacamole

• 把一半的洋葱和香菜的一半on a cutting board (or in a molcajete, or mortar, if you have one) along with the chile and salt. Mince together with a large knife and mash with the side of the knife to create a paste (or mash with the pestle). Transfer to a bowl. Score the avocado, twist the halves apart, and scrape the flesh out of its skin with a large spoon into the bowl. Add the remaining onion and cilantro and stir together with a fork.

• Peel the potatoes and cut them into 1⁄2-inch dice. Cook in a saucepan of boiling salted water until they are just cooked through and still hold their shape, about 5 minutes. Drain.
• Remove the casings from the chorizo and crumble (Mexican) or finely chop (Spanish) the meat. Cook the chorizo in a large skillet (add a tsp. of oil if using Spanish chorizo) over medium heat, stirring, for 5 minutes. Add the potato and oregano and cook, stirring, for 5 minutes. Season with salt to taste.
• Make tacos with the tortillas, guacamole, and queso fresco, if using.