Preparation Cook beans in a medium saucepan of boiling salted water (2 teaspoon salt for 2 quarts water), uncovered, until crisp-tender. Drain and transfer to an ice bath to cool. Pat dry. Whisk together mustard, shallot, vinegar, oil, 1/4 teaspoon salt, and 1/8 teaspoon pepper and toss with beans. Stir together eggs, mayonnaise, celery, chives, lemon zest and juice, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Divide arugula among jars and layer beans, salmon, and egg salad on top. Cooks' note:Assembled jars can be chilled up to 6 hours. Serve at room temperature.