Although you may need to make a trip to the Asian market to pick up miso and mirin, look for wasabi powder in your supermarket's spice aisle; it's much milder than the kind found in Japanese markets.
1/4 cup yellow miso (soybean paste)
1/4 cup mirin (sweet rice wine)
1/4 cup dry white wine
1 tablespoon wasabi powder
1 tablespoon rice vinegar
1 (1-pound) flank steak, trimmed
How to Make It
Combine first 5 ingredients in a small bowl; stir well with a whisk. Combine miso mixture and steak in a large zip-top plastic bag. Seal and marinate in refrigerator 2 hours.
Prepare grill or broiler.
Remove steak from bag, reserving marinade. Place steak on grill rack or broiler pan coated with cooking spray. Grill or broil 6 minutes on each side or until desired degree of doneness, basting occasionally with reserved marinade.