Preheat the oven to 350°F (175°C). Grease and flour an 8.5 x 4.5 inch loaf pan.
In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
Using a stand mixer with the paddle attachment, beat the butter, sugar, and vanilla on medium-high speed until smooth and pale, about 3-4 minutes.
Add eggs, one at a time, beating until incorporated.
On low speed, alternate adding half the flour mixture and half the milk. Repeat with the remaining flour mixture and milk, mixing just until combined.
In a small bowl, combine the brown sugar, cinnamon, and apples for the apple mixture.
Pour half the batter into the prepared loaf pan. Top with half of the apple mixture. Swirl gently with a knife or skewer.
Pour the remaining batter on top and add the remaining apple mixture. Swirl again lightly.
In a small bowl, mix the brown sugar and cinnamon for the topping, then sprinkle over the batter.
Bake for 45-55 minutes or until a toothpick inserted into the center comes out clean with a few moist crumbs attached.
Cool the bread in the pan for 15-20 minutes, then transfer to a wire rack to cool completely.
For the glaze, whisk together confectioners’ sugar, cinnamon, and water. Drizzle over the cooled bread before slicing.