Combine coffee mixture, soy sauce, olive oil, sugar, vinegar, garlic and pepper in a non-reactive dish large enough to hold steak or in a gallon-size resealable plastic bag. Pierce steak all over with fork; add steak to coffee marinade and turn to coat.

Preheat grill to medium-high heat. Add steak; cover and cook for 5 to 7 minutes on each side for rare to medium-rare.

Transfer to cutting board; let steak rest for 5 minutes. Cut steak against the grain into ¼-inch-thick slices. Serve topped with chimichurri sauce, if desired.