In a large resealable plastic bag, combine all the ingredients except the flank steak, shaking well to mix.
Add the flank steak, turn to coat with the marinade. Refrigerate for at least 20 minutes or overnight, turning the bag occasionally.
When ready to cook, coat the grill rack with cooking spray. Prepare the grill to medium-high heat. Snip a corner of the bag with scissors and drain the marinade into a small saucepan; set aside.
Place the steak on the prepared grill and cook for 5 minutes on each side, or until desired doneness. Let stand 5 minutes before thinly slicing diagonally across the grain. Transfer to a serving platter.
Meanwhile, bring the reserved marinade to a boil over medium-high heat and continue boiling 3 minutes, or until slightly thickened. Drizzle over sliced steak.