To prepare dressing: Whisk shallot, broth, oil, vinegar, mustard, salt and pepper in a small bowl.
To prepare salad: Toast walnuts in a small dry skillet over medium-low heat, stirring, until fragrant, 2 to 3 minutes. Transfer to a small bowl and let cool.
Just before serving, cut pears into 16 slices each. Place in a large bowl. Spoon on 1 tablespoon of the dressing and toss to coat. Add lettuce, arugula and the remaining dressing; toss well. Divide among 8 plates. Top with the walnuts.