Make the rub by combining the chili powder, paprika, cumin, oregano, coriander, garlic powder, salt, black pepper, onion powder, and cayenne pepper in a small bowl and mix thoroughly.
Rub the flank steak with olive oil on both sides, then season both sides well with the rub. Side Note: Store any remaining rub in an airtight container.
Remove the flank steak from the refrigerator 20 minutes before cooking.
Heat a grill pan on medium-high heat and coat with olive oil cooking spray.
Add the flank steak for 5-7 minutes per side, or until cooked to your desired degree of doneness, using a meat thermometer.
Let the meat rest for 5 minutes. Thinly slice the meat against the grain.