Make the phyllo: In a large bowl, combine flour and salt. Make a well in the center, and add 1 1/2 cups warm water, 1/4 cup olive oil, and vinegar. Using a fork, work flour into the liquid until incorporated. Knead dough in bowl until it comes together, adding more flour if necessary, about 10 minutes. Cover, and let rest at room temperature for 30 minutes.
In a large skillet, heat 2 tablespoons olive oil over medium heat. Add scallions and onions, and saute until wilted, about 10 minutes. Add mixed greens, and saute until wilted, about 2 minutes. Transfer to a large bowl, and add dill, parsley, mint, and chervil. Season with salt and pepper. Sprinkle trahana over filling, and combine.
Preheat oven to 350 degrees F.
Lightly brush a 12 1/2 by 2-inch round cake pan with olive oil. Divide dough into 6 equal pieces. On a lightly floured surface, roll 1 piece of dough into a 6-inch round with a rolling pin. Roll dough out and onto itself around a 24-inch dowel, rotating dough frequently. (You should be able to see your hands through the dough.) Transfer dough to a work surface dusted with cornmeal. Repeat rolling-and-rotating process with remaining dough, stacking each on top of the other, dusted with cornmeal.
Fit 1 sheet of phyllo dough into prepared pan. Brush with olive oil, and repeat with 2 more sheets of phyllo. Place scallion-onion filling on top of phyllo, spreading evenly. Drizzle with remaining 1 tablespoon olive oil. Top with remaining 3 sheets phyllo, brushing between layers with olive oil. Trim top and bottom crusts to create a 2-inch border around the perimeter of the loaf. Using a sharp knife, score pie through top and bottom crust in a diamond pattern.
Transfer to oven, and bake until filling is set and crust is golden brown, about 1 hour. Let cool on a wire rack for at least 1 hour before serving.
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