Let steak stand at room temperature for 30 minutes.
In a small bowl, stir together brown sugar, garlic powder, chili powder, salt, pepper, dry mustard, and cumin. Generously sprinkle mixture all over steak; let stand for 15 minutes.
Heat a large grill pan over medium-high heat; spray pan with cooking spray. Add steak, and cook until an instant-read thermometer inserted in thickest portion registers at least 130° to 135°, 5 to 7 minutes per side, or to desired degree of doneness. Let stand for 10 minutes; slice steak against the grain. Serve with Chimichurri Sauce.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/grilled-flank-steak-with-chimichurri-sauce-recipe/