Place flank steak in a resealable plastic bag. Combine remaining ingredients and pour over steak. Seal bag and refrigerate overnight.
Preheat grill for medium-high heat. Remove steaks from bag making sure to reserve marinade. Place marinade in a small saucepan and bring to a boil, reduce heat and allow to simmer for 6-8 minutes. Place flank steaks on a lightly oiled grill grate and cook for 6 minutes per side. Remove from heat, drizzle with sauce, and serve.