1) Peel and slice red onions thinly. Add them to a bowl with the lime juice and a good pinch of salt. Cover and let marinate for at least 30 minutes while you make the rest of the fillings.
2) Chop up the yam and poblano peppers. Try to chop both into long matchsticks of roughly the same size.
3) Remove casing from chorizo if it has it on and start browning it in a skillet over medium high heat.
4) Once chorizo is cooked, add in poblanos and yams and cook until they start to soften.
5) Warm your tortillas in a hot skillet for a few seconds per side or you can do them in a large batch in the oven by wrapping them in foil and baking them for a few minutes at 350 degrees.
6) Add chorizo filling to a few tortillas and top with crumbled cheese and marinated onions.