Preheat your oven to 350°F (175°C) and prepare a loaf pan by greasing it or lining it with parchment paper.

In a large bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.

In another bowl, combine the sugar, vegetable oil, eggs, and vanilla extract. Mix until well blended.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Avoid over-mixing.

Fold in the diced apples gently into the batter until evenly distributed.

In a small bowl, combine brown sugar and cinnamon to create the filling mixture.

Pour half of the batter into the prepared loaf pan, sprinkle half of the brown sugar-cinnamon mix over it, then add the remaining batter and top with the rest of the filling mixture.

Using a knife, create a gentle swirl pattern where the filling is layered.

Bake for about 45-55 minutes, or until a toothpick inserted in the center comes out clean.

Allow to cool in the pan for about 10 minutes before transferring to a wire rack to cool completely.

While the bread cools, whisk together powdered sugar and milk for the glaze. Drizzle it over the cooled bread before serving.