Preheat your oven to 350°F (175°C). Grease and flour the loaf pan or line it with parchment paper for easy removal.
In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, baking soda, salt, and 2 teaspoons of ground cinnamon.
In another bowl, beat the eggs and then add in the melted butter and buttermilk. Mix well.
Gradually add the wet ingredients to the dry ingredients, stirring until just combined. Do not overmix.
Gently fold in the chopped apples, ensuring they are evenly distributed.
In a small bowl, combine the brown sugar and 1 tablespoon of ground cinnamon to create the filling.
Pour half of the batter into the prepared loaf pan, then sprinkle half of the cinnamon sugar filling on top.
Pour the remaining batter over the filling and then sprinkle with the remaining cinnamon sugar mixture.
Using a knife or spatula, swirl the batter gently to mix in the filling without fully combining.
Bake in the preheated oven for about 50 minutes, or until a toothpick inserted in the center comes out clean.
Allow the bread to cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.