Preheat oven to 450 degrees.
Cover steak with seasoning mix and salt, rubbing in well.
Let sit at room temperature for at least 30 minutes.
Once the oven is hot, place a skillet that's large enough to hold flank steak in the oven for 30 minutes. This heats the skillet completely.
Place steak in the skillet to cook. It's fine if it comes up the interior sides; it just can't spill over.
Cook for 5 minutes and flip.
Cook an additional 4 minutes.
Remove skillet from oven and place on heat-proof surface.
Cover with foil for 10 minutes.
Slice thinly across the grain.