Green Bean and Tomato Salad with Buttermilk Dressing

Name: Green Bean and Tomato Salad with Buttermilk Dressing
Ingredients: ½ cup buttermilk; 2 teaspoons fresh lemon juice; ½ teaspoon garlic powder; ½ teaspoon onion powder; 3 tablespoons olive oil, divided; Kosher salt and freshly ground black pepper; 1 pound wax or green beans, trimmed; 2 large leeks, white and pale-green parts only, halved, cut into 4” pieces; 1 pint cherry tomatoes, halved; 1 large heirloom tomato, sliced; ½ cup thinly sliced fresh mint leaves; ¼ cup chopped fresh chives