On a baking sheet, bake sweet potatoes for 1 hour or until done. Let cool, then peel and mash. Reduce oven to 350°F.
In a large mixing bowl, combine mashed sweet potatoes, Splenda Sweetener, flour, milk, orange juice, egg, vanilla extract, 2 tablespoons orange zest, and ¾ cup melted butter. Using an electric mixer, beat on medium speed until smooth. Transfer to hotel pan.
In a bowl, combine breadcrumbs, pecans, syrup, 2 teaspoons orange zest, and ½ cup melted butter. Sprinkle over top of casserole.