Place first 8 ingredients in a 2-gal. zip-top plastic freezer bag; squeeze bag to combine. Add steak; seal bag, and chill 4 to 12 hours. Remove steak from marinade, discarding marinade.
Preheat grill to 400° to 450° (high) heat. Grill steak, covered with grill lid, 9 minutes on each side or to desired degree of doneness. Remove from grill, and let stand 10 minutes. Cut diagonally across the grain into thin slices. Season with salt and pepper to taste. Top with Watermelon Salsa.