Add all of the ingredients for the marinade to a small blender and blend until combined. If you don’t own a blender, stir the ingredients together in a bowl.

Transfer the flank steak and the marinade to a large 1 gallon zip lock bag. Seal the bag and marinate the steak for at least 1 hour (ideally several hours, up to 24 hours).

When you’re ready to cook the steak, heat 2 tablespoons of avocado oil (or olive oil or cooking oil of choice) in a large (12-inch or larger) skillet over medium-high heat. Allow the skillet to heat up for a few minutes, until the oil is sizzling hot.

Remove the flank steak from the marinade and allow the excess marinade to drip off of it over the sink. Carefully place the flank steak in the hot skillet and cook for 7 to 8 minutes per side, until the steak reaches your desired level of doneness. Insert a meat thermometer into the thickest part of the meat to check the internal temperature. Go for 125 to 130 degrees Fahrenheit for medium-rare if you're looking for tender steak. Shoot for 130 to 135 degrees for medium, and 140 degrees or higher for well-done.

Transfer the steak to a large cutting board and let steak rest for 15 minutes.

Slice the flank steak against the grain using a sharp knife in thin slices.

Heat up the tortillas using your preferred method.

Load up the tortillas with sliced flank steak, avocado, red onion, cotija cheese, and fresh cilantro with a drizzle of your favorite store-bought or homemade salsa. Serve and enjoy!