Preheat oven to 400 degrees F. Cook pasta according to package directions, adding green beans the last 5 minutes of cooking. Drain pasta mixture; rinse with cold water. Drain and set aside. Meanwhile, toss bagel pieces with 1 tablespoon oil in a 15x10x1-inch baking pan. Bake for 8 to 10 minutes or until golden brown, stirring once. Remove and cool in pan on a wire rack.
For vinaigrette, in a medium saucepan whisk together vinegar, mustard, and salt until combined. Slowly whisk in 3/4 cup olive oil. Heat over medium-low heat just until warm, whisking constantly. Remove from heat. Stir in red onion and capers.
Place pasta mixture, romaine, mozzarella balls, smoked salmon, and bagel croutons in a very large bowl. Drizzle vinaigrette over mixture in bowl; toss to combine. Sprinkle with cracked black pepper. Serve immediately.