Preheat oven to 375°.
Unroll dough, separating into strips. Let rest 5 minutes. Working on a flat surface, coil one strip of dough around itself in a spiral pattern. Add second strip of dough to end of first strip, pinching ends together to seal; continue coiling dough. Repeat procedure with remaining dough strips. Let rest 5 minutes. Roll into a 13-inch circle; fit into a 9-inch pie plate coated with cooking spray. Fold edges under; flute.
Heat the oil in a large nonstick skillet over medium-high heat. Add the leek, pepper, and potato; sauté 4 minutes. Spread leek mixture into prepared crust.
Place the milk, egg substitute, cheeses, and mustard in a blender, and process until smooth. Pour milk mixture over leek mixture. Bake at 375° for 40 minutes; let stand for 10 minutes.