Combine flour and salt in a medium bowl. Add oil, stirring until crumbly. Combine cold water and lemon juice. Sprinkle mixture, 1 tablespoon at a time, over surface of flour mixture. Toss with a fork until dry ingredients are moistened. Press dough into a 4-inch circle on plastic wrap. Cover with another sheet of plastic wrap, and chill 5 minutes.
Roll dough into an 11-inch circle. Place in freezer 5 minutes or until top sheet of wrap can be easily removed. Invert dough into a 9-inch pieplate coated with cooking spray, and remove remaining sheet of plastic wrap. Fold edges under and flute, if desired.
Combine pumpkin and next 7 ingredients in a large bowl; stir well. Pour mixture into pastry shell. Bake at 350° for 1 hour or until a knife inserted in center comes out clean. Cool completely on a wire rack. To serve, cut into 10 slices, and top each with 1/4 cup frozen yogurt.