Combine spices into a small bowl and mix. Coat both sides of flank steak with the spice rub. Be sure to coat the edges as well.
Place the steak into your preheated smoker. Smoke at 225°F for about 45 minutes or until the internal temperature reaches 125°F.
Reverse sear the steak for a great finish.
You can either use a grill or a hot pan on a stove. Crank the grill or stove to high heat. Sear the flank steak on both sides for about 1 minute. This will give you a final internal temperature of 135°F for medium rare. You can cook it longer if you prefer a more well level of doneness.
Let the steak rest for 10 minutes, then slice against the grain and serve.