Combine walnuts, garlic and salt in a food processor and blend until finely ground. (If preferred, walnuts, garlic and salt can be pounded into a paste with a mortar and pestle.) Combine walnut mixture, oil and vinegar in a salad bowl and whisk until blended.
Cook green beans in boiling salted water until crisp-tender, 4 to 6 minutes. Drain well, rinse with cold water, spread on a dish towel and pat dry.
Add green beans, tomatoes, onion, cucumber, cilantro, dill and mint to walnut dressing and toss to blend.
Whole World Vegetarian