Preheat the oven to 400 degrees F. Position a rack in the center of the oven.
Whisk together the yogurt, chopped mint and 1 teaspoon of the olive oil in a small bowl and set the yogurt dressing aside.
In a large bowl, toss the watercress, torn basil leaves, dill sprigs, chives, scallions, cucumber, radishes, feta cheese and walnuts together with the lemon juice, to taste. Season the salad with salt and pepper.
Lay the lavash on a baking tray and toast bread on the center rack until warmed through, 2 to 3 minutes per side.
To serve, mound the salad on one side of the warm bread and drizzle with the yogurt sauce. Fold the bread over the salad and slice the sandwiches in half on the bias. Serve immediately.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.