Mix all marinade ingredients in a small bowl or liquid measuring cup. Place flank steak in a large zip lock bag and add the marinade, coating the steak well. Seal bag and refrigerate for 2-8 hours (the longer you marinate, the more flavor you'll have!)Flip the bag a few times while marinating to coat the meat well.
Remove meat from refrigerator and place on counter to bring to room temperature for 30-60 minutes. This helps the steak cook more evenly. Next, remove the steak from the bag and discard the marinade. Grill steak 4 minutes per side for medium-rare (or longer, if preferred.)
Let meat rest for 5 minutes before cutting into thin slices.