Place sweet potatoes in a medium saucepan with enough water to cover. Cook over medium-high heat until tender, about 25 minutes. Drain off water. Transfer potatoes to a food processor or blender and puree with 1 tablespoon butter or margarine.
Saute scallions in 1 to 2 tablespoons butter or margarine for 1 minute. Combine in a medium bowl, pureed potatoes, sauteed scallions, eggs (or Egg Replacer), 1 cup bread crumbs, pepper, salt, zest, and parsley. Mix well and set aside.
In a small skillet, melt remaining 1 tablespoon butter or margarine. Add remaining 2 tablespoons bread crumbs and toast over medium-high heat.
Preheat oven to 350 degrees F. Spoon stuffing mixture into an oval baking dish. Sprinkle toasted bread crumbs over stuffing and bake 20 minutes, or until set. Serve hot.