How to Make It
Fill a large pot with salted water. Bring water to a boil; add green beans. Cook green beans in boiling water until crisp-tender, about 3 minutes. Transfer beans to a bowl of ice water to stop cooking, then drain and let cool. Cut beans in half crosswise and set aside.
In a small bowl, combine shallots, garlic, Dijon, vinegar, salt, and pepper. Slowly whisk in olive oil. Set vinaigrette aside.
In a large bowl, combine green beans with tomatoes and walnuts. Crumble over cheese and serve at room temperature or slightly warmed.