1. Preheat oven to 350°. Slice tomatoes into 1/4-inch-thick slices. Arrange tomato slices on several layers of paper towels over a wire rack. Sprinkle with 2 teaspoons salt; cover with more paper towels, pressing gently. Let salted tomatoes stand 1 hour, replacing paper towels on top and bottom after 30 minutes.
2. Combine cheese, mayonnaise, herbs, pepper, and onion in a medium bowl; stir well, and set aside. Roll piecrust into a 13-inch circle on a flat surface. Fit into a 9-inch pie plate; fold edges under, and crimp. Firmly pat tomato slices dry with additional paper towels. Arrange tomato slices in piecrust; top with cheese mixture.
3. Bake at 350° on lowest oven rack for 40 minutes or until golden brown. Cool completely on a wire rack.