Heat oven to 350°F. Grease 13x9-inch pan. Lightly spoon flour into measuring cup; level off. In large bowl, combine flour, sugar, baking powder, salt and orange peel. Using fork or pastry blender, cut in margarine until crumbly. Add milk, vanilla and eggs; stir until well blended. Pour 3/4 of batter(2 1/4 cups) into greased pan. Top with peaches and blueberries. Spoon remaining batter over fruit.
Bake at 350°F. for 35 to 45 minutes or until edges are golden brown. Cool 30 minutes. In small bowl, blend all icing ingredients, adding enough milk for desired drizzling consistency. Drizzle over coffee cake.