8 white corn tortillas (or any taco shell of your choice!)
cilantro (optional for garnish)
for the quick pickled red onions
In a small sauce pan add the sliced red onions, water, white vinegar and sugar. Bring mixture to a boil and then turn off the heat. Let the onions sit for at least 15 minutes to pickle.
for the tacos
Season steak with salt and pepper on both sides. Preheat a large caste iron skillet or grill over high heat. Add in a high-heat oil (avocado works well!) to coat the surface of the pan.
Carefully place steak in pan and cook for 1 to 2 minutes on each side, creating a nice, even char. Sear steak around the edges, as well, to seal in all the juices and flavor. To tell if your steak is done, use a meat thermometer to check the internal temperature. The steak should be at 135°F for medium rare, 140°F for medium, or 145°F for medium well.
Take the steak off the heat and let it rest for least 15 minutes before slicing into 1/4 thick slices to use in your tacos.
To char the tortillas, turn your oven to broil. Place tortillas on a large baking sheet, then place in the oven for about 30 seconds. Remove from oven, flip the tortillas over, and repeat on the other side.
To assemble the tacos, take one tortilla and lay it flat. Place desired amount of steak onto the tortilla, sliced avocado, crumbled cheese, some pickled onions and jalapeño slices. Spoon chimichurri sauce over the filling. Repeat with the remaining tacos.