To prepare salad, place the beef on grill rack coated with cooking spray, and grill 7 minutes on each side or until desired degree of doneness. Let stand 10 minutes. Cut the steak diagonally across grain into thin slices. Place beef in a large bowl.
Bring water to a boil in a saucepan; add beans. Cover and cook 3 minutes or until crisp-tender. Rinse with cold water; drain well. Add beans, watercress, tomatoes, onion, mushrooms, and hearts of palm to beef, and toss gently to combine.
To prepare dressing, combine red wine vinegar and remaining ingredients, stirring well with a whisk. Drizzle dressing over salad; toss gently to coat.
This recipe is great with leftover beef.