In a small bowl, mix the coffee, chili powder, paprika, salt, cumin, coriander, granulated onion, granulated garlic, and sugar. Liberally coat the flank steak with the rub, patting with your fingers so it adheres.
Preheat gas or charcoal grill to medium-high heat. Grill the steak for 4 to 5 minutes per side for medium doneness. Remove from the grill and let rest for at least 15 minutes.
To serve, slice steak against the grain.
