To prepare dressing, combine first 5 ingredients in a bowl; stir well with a whisk.
To prepare steak, heat a large nonstick skillet or grill pan coated with cooking spray over medium-high heat. Rub both sides of steak with pepper. Add steak to pan; cook 6 minutes on each side or until desired degree of doneness. Remove from pan; place on a cutting board. Cover loosely with foil; let stand 5 minutes. Cut steak diagonally across grain into thin slices. Place steak in a bowl. Drizzle with half of dressing, and toss well.
To prepare salad, combine watercress and next 5 ingredients (watercress through carrot) in a large bowl. Drizzle with remaining dressing, and toss well. Divide salad evenly among 6 plates; arrange steak evenly over salad. Sprinkle each serving with 1 teaspoon peanuts.