Heat barbecue to medium-high.
Using a mortar and pestle, combine coffee, hot pepper flakes, salt, sugar and garlic; grind until fine. Rub all over steaks and let marinate for 15 minutes.
Brush steaks with some of the sunflower oil; place on greased grill. Cook, covered flipping once, until desired doneness, 5 to 6 minutes per side for medium-rare. Transfer to cutting board; cover with foil and let stand for 10 minutes before serving.