Transfer the chiles, cumin and coriander seeds to a coffee grinder. To fit them into the grinder's compartment, it may be necessary to rip the chiles into pieces. Process into a fine powder.
Smash the garlic. Slice the pork butt into 1/2 inch cubes. Place them into a zip-lock bag - along with the chile/cumin/coriander powder, Mexican oregano, garlic and salt to taste. Pour in the vinegar and massage the bag until well combined. Cover and marinate the pork mixture in the refrigerator overnight.
Grind the pork mixture in a food processor until it reaches a consistency - somewhat coarser than store-bought hamburger.
Slice the onion thinly. Over a medium-high flame, heat up a large iron or aluminium skillet, add peanut oil, chorizo and sliced onions. With a metal spatula, chop and turn the chorizo/onion mixture until it is cooked - thoroughly. Serve in pre-warmed tortillas, topped with your choice of cilantro, pineapple chunks, green salsa, hot sauce, etc.