In a small bowl, combine the sugar, salt, black pepper, red pepper flakes, mushroom powder, garlic and 1/4 cup olive oil, and stir well to form a thick paste with the consistency of wet sand.
Rub the paste all over the steak, coating it evenly. Wrap tightly in plastic wrap and refrigerate for at least 12 hours, or overnight.
About 1 hour before grilling, remove the steak from the refrigerator and brush off the excess marinade with a paper towel. Place on a plate and let come to room temperature.
Preheat a gas grill or prepare a fire in a charcoal grill (use enough coals to keep the fire going for about 25 minutes).
Put the steak on the hottest part of the grill, cover and cook, turning every 5 to 8 minutes, for about 25 minutes for medium-rare; the internal temperature should be 125 degrees. Transfer to a carving board and let rest for 10 to 15 minutes.