In small mixing bowl combine flour, water, oil, and dash salt; using hands, knead dough to form a smooth ball (dough should hold together but not be sticky; if necessary, add up to 1 more tablespoon warm water to adjust consistency).
Wrap dough in plastic wrap and set aside while preparing filling (plastic wrap will prevent dough from cracking).
In small nonstick skillet heat margarine until bubbly and hot; add scallions and saute over low heat until soft.
Set aside.
In work bowl of food processor or in large mixing bowl combine mashed potatoes, cottage cheese, 3 eggs, 1 teaspoon salt, and the pepper; process, or beat with electric mixer, until smooth.
Stir in sauteed scallions.
Preheat oven to 350°F.
Between 2 sheets of wax paper roll dough, forming a rectangle about 1/8 inch thick; remove paper and fit dough into a 10 x 6 x 2-inch baking dish so that edges of dough extend slightly over sides of dish.
Spoon potato mixture over dough and bring up sides of dough over edges of filling, leaving center uncovered.
In small bowl beat remaining egg with Parmesan cheese; pour over entire surface of torte.
Bake until browned, 35 to 40 minutes.
Remove from oven and let stand until set, about 15 minutes.