Preheat the oven to 350 degrees F. Spray a 13x9-inch pan with nonstick spray.
In a large bowl, whisk together the flour, sugar, baking powder, salt and orange zest. Cut the butter into the mixture with a pastry blender until fine crumbs form. Add the milk, eggs and vanilla. Stir until well blended.
Pour 3/4 of the batter into the prepared pan. Top with fruit, spreading out evenly.. Spoon the remaining batter over the fruit.
Bake 35 to 45 minutes, until golden brown. Let cool.
PREPARE THE GLAZE:
In a medium bowl, whisk together glaze ingredients (add enough milk to create a good drizzle consistency); drizzle over the cooled cake.
For a more decorative look, you can dot the peaches and blueberries on top of the batter instead of burying it inside the batter.