Bring 2 quarts water and salt to a boil. Add green beans; cook 4 minutes or until beans are crisp-tender. Drain and rinse with cold water; drain. Combine green beans, shallots, peppers, chickpeas, and garlic in a large bowl.
Combine mayonnaise, vinegar, and paprika in a small bowl, stirring well. Add mayonnaise mixture to bean mixture; toss gently to combine. Arrange 1 cup arugula on each of 4 plates; top each serving with about 1 cup bean mixture. Divide tuna evenly among plates.
Sprinkle cheese evenly over bread slices; place bread on a baking sheet. Broil 2 minutes or until lightly toasted. Serve toasts with salad.