In a medium bowl, stir together 1 cup flour, cornmeal, and salt. Using a pastry blender, cut in vegetable oil spread until pieces are pea-size. Sprinkle 1 tablespoon cold water over part of the flour mixture; gently toss with a fork. Push moistened dough to the side of the bowl. Repeat moistening flour mixture, using 1 tablespoon cold water at a time, until all flour mixture is moistened (3 to 4 tablespoons cold water total). Shape dough into a ball.
Preheat oven to 375°F. Line a baking sheet with foil; sprinkle lightly with 2 teaspoons flour or as needed. Place Cornmeal Pastry on foil. Slightly flatten dough ball. Using a rolling pin, roll dough from center to edges into a 12-inch circle. Set aside.
In a large bowl, stir together cornstarch, lemon peel, and cinnamon. Add plum slices and peach slices. Toss to coat. Drizzle with honey; toss gently to coat. Mound fruit mixture in center of pastry circle, leaving a 2-inch border around the edges. Fold border up over fruit slices, pleating dough as needed. Brush pastry lightly with milk.
Bake for 30 to 40 minutes or until fruit slices are tender and pastry is lightly browned. If necessary to prevent fruit from drying out, cover tart with foil for the last 10 to 15 minutes of baking. Cool for 30 minutes and serve warm. (Or cool completely.) Cut into 10 slices, and serve with whipped topping.