Combine first 5 ingredients in a small bowl; set aside.
Brush olive oil evenly over steaks. Rub anise seed mixture over both sides of steaks. Prepare grill. Place steaks on grill rack; grill 5 minutes on each side or until fish flakes easily when tested with a fork. Set aside.
Combine the watercress and onion in a large bowl. Combine the vinegar and next 6 ingredients (vinegar through black pepper) in a jar. Cover tightly, and shake vigorously. Pour over the watercress mixture, and toss gently. Arrange watercress mixture on a platter, and top with steaks. Sprinkle the steaks with toasted sesame seeds.