Combine the olive oil, soy sauce, green onion, minced garlic, lime juice, red pepper flakes, cumin, and brown sugar in a food processor or blender, then puree.
Pour the marinade over the flank steak in a large zip-lock bag, then seal and place it in the refrigerator for 6-24 hours.
Remove the meat from the refrigerator at least 20 minutes before grilling/cooking.
Preheat the grill pan over medium-high heat, and coat it with olive oil cooking spray.
Once the pan is hot, add the flank steak and cook for 4-5 minutes on each side or until it's cooked to your desired degree of doneness.
Let the meat rest for at least 5 minutes before slicing it against the grain. Enjoy.