Preheat your oven to 350°F (175°C) and grease a 9x5-inch loaf pan.

In a large bowl, whisk together all-purpose flour, granulated sugar, baking powder, salt, and ground cinnamon.

In a separate bowl, whisk together eggs, vegetable oil, vanilla extract, and milk until smooth.

Pour the wet ingredients into the dry ingredients and stir gently until just incorporated.

Fold in the diced apples, ensuring they are evenly distributed.

Pour half of the batter into the loaf pan, sprinkle half of the cinnamon sugar, then add the remaining batter followed by the remaining cinnamon sugar.

Swirl through the batter with a knife to create a marbled effect.

Bake for 50-60 minutes, until a toothpick comes out clean.

Let cool in the pan for 10 minutes, then transfer to a wire rack.

Prepare glaze by whisking powdered sugar, milk, and vanilla extract, then drizzle over the cooled bread.