How to Make It
Preheat the oven to 350°. Spread the walnuts in a pie plate and toast for about 10 minutes, until golden. Let cool.
Meanwhile, bring a large saucepan of salted water to a boil and fill a bowl with ice water. Add the green beans to the boiling water and blanch until crisp-tender, about 3 minutes. Using a slotted spoon, transfer the beans to the ice water. Add the squash to the boiling water and blanch until crisp-tender, about 1 minute. Add the squash to the ice water. Drain the vegetables and pat completely dry.
In a blender, combine the walnuts, yogurt, walnut oil, lemon juice, cilantro, chives and tarragon. Blend until smooth, scraping down the side of blender. Transfer the dressing to a bowl and season with salt and pepper. Add the green beans, squash and tomatoes, toss to coat and serve.