This dinner salad is so easy to prepare: slice the cheese and leftover steak, whisk together an herb dressing, and saute the vegetables.
Make dressing: In a small bowl, whisk together parsley sauce and vinegar. Set aside.
In a large nonstick skillet, heat oil over medium-high heat. Add onion; cook, stirring occasionally, until lightly golden, 2 to 4 minutes.
Add green beans and 1/2 cup water. Season with salt and pepper; cover, and cook until beans are tender, 5 to 6 minutes. Uncover; cook until vegetables are browned, about 3 minutes more. Remove from heat.
In a large bowl, gently toss lettuce with half the dressing. Divide among 4 plates. Arrange beef, cheese, and vegetables over lettuce. Drizzle with remaining dressing, and season with salt and pepper.
Boston or Bibb?Also called butter lettuce, both Boston and Bibb have soft, delicate leaves; heads of Bibb tend to be smaller.