In a small bowl combine the coriander, five-spice powder, chili powder, cinnamon, sea salt, and brown sugar. Rub both sides of the flank steak with the mixture and let sit for 1 to 2 hours, covered, in the refrigerator.

Preheat grill to medium and grill for 5 to 6 minutes per side, until the meat is browned with nice grill marks. Allow the meat to rest for 10 minutes before slicing.

Slice on the bias (at a 45-degree angle) into 1/4-inch slices.