Whisk together first 8 ingredients. Pour half of marinade into a large zip-top plastic freezer bag, and add chicken breasts; seal bag. Repeat procedure with remaining marinade and flank steak. Chill 2 hours.
Preheat grill to 350° to 400° (medium-high) heat. Remove beef and chicken from marinade, discarding marinade.
Grill chicken and steak at the same time. Grill steak, covered with grill lid, 10 minutes on each side or to desired degree of doneness; grill chicken, covered with grill lid, 5 to 6 minutes on each side or until done.
Remove from grill, and let stand 10 minutes. Cut steak and chicken diagonally into 1/4-inch-thick strips.