In large mixing bowl stir together: flour, oats, brown sugar and baking soda. Melt butter or margarine over low heat and stir in until well blended. Set aside 2 cups of this mixture.
Distribute remaining oat mixture evenly into an ungreased 15 X 10 X 1 inch baking pan and pat down. Bake this in a 350 degrees F (175 degrees C) oven for 12 minutes.
Stir lemon OR orange peel into mincemeat OR fruit-pie filling. Spread filling carefully over the HOT baked crust. Sprinkle the reserved oat mixture over the filling. Pat oat mixture very gently onto filling.
Bake for 20 to 25 minutes or until top is golden. Cool pan on rack. Drizzle with icing.:
To Make Icing: Mix together 1 cup confectioners' sugar, 1/4 teaspoon vanilla, and 1 to 2 tablespoon milk. Add milk a little at a time to obtain drizzling consistency.