For the marinade:
1) In a non-reactive dish or large re-sealable plastic bag, combine all ingredients except steak and mix thoroughly.
2) Add steak and turn to thoroughly coat. Cover dish or close bag and allow to marinate at room temperature for 30 minutes. (If you are making ahead, cover, and place in refrigerator. Can be marinated up to 24 hours in refrigerator.)
For the grilled flank steak:
1) Once steak has marinated, remove from refrigerator and bring to room temperature for at least 15 minutes. Preheat a lightly oiled griddle pan to medium-high heat.
2) When griddle pan is heated, remove steak from marinade, shake off excess, add to pan and cook for about 6 to 8 minutes per side for medium rare.
3) Transfer to a cutting board, season with additional salt and freshly ground black pepper and let rest for 10 to 15 minutes. Slice thinly across the grain and serve.