1. In a small bowl, combine the soy with 2 tablespoons of the olive oil, sugar, garlic and sesame oil. Transfer the marinade to a zippered plastic bag and add the flank steak, turning to coat. Seal the bag and marinate at room temperature for 1 hour or in the refrigerator for up to 8 hours.
2. Preheat a grill or grill pan. Remove the steak from the marinade and pat dry. Rub both sides with 1 tablespoon of the oil and grill over high heat for 4 to 5 minutes per side for medium-rare meat at the thickest part. Transfer to a cutting board and let rest 5 minutes. Thinly slice the meat against the grain and serve.