Boil a large pot of water. Add 1 tablespoon salt and the green beans and cook until very tender, 6 to 8 minutes. Drain and run under cold water to cool. Rub the beans vigorously between your hands to break them in half lengthwise. Transfer to a bowl.
Whisk together the mustard, vinegar, oil, 1/4 teaspoon salt, and 1/4 teaspoon pepper. Drizzle over the green beans. Sprinkle with the almonds.