Remove steak from refrigerator to bring to room temperature for about 30 minutes prior to cooking. Pat both sides dry with paper towel.
In a small bowl, mix spice rub, then pat the rub evenly onto the surface of the steak.
In a large non-stick skillet or cast-iron skillet, heat 1 tablespoon of vegetable oil over medium-high heat until the oil is sizzling hot.
Lay steak in the hot pan. Sear for 3-4 minutes per side for a medium rare finish.
Remove steak from the pan when the internal temperature reads 125 degrees Fahrenheit using a meat thermometer in the thickest part of the steak.
Allow the steak to rest on a cutting board for 5-10 minutes, before cutting it into 1/2-inch thin slices against the grain of the meat.
Serves strips of cooked flank steak with tortillas, onions, cilantro, salsa and a squeeze of lime juice.
Notes
If your cut of flank steak does not fit in your largest skillet, divide the meat into 2 pieces of equal size and cook in batches.You can also use a grill pan to cook the steak. For the oil, choose vegetable oil, canola oil, avocado oil or any other neutral tasting oil that has a high smoke point. Do not use olive oil.