Preheat the oven to 375 degrees Fahrenheit.

Grease a 9" square cake pan.

Combine all the ingredients in a small bowl.

Mix well with a fork until everything is combined. Set aside.

Whisk together the flour, baking powder, and cinnamon in a large bowl. Set aside.

Whisk together the egg, melted butter, and milk until thoroughly combined.

Pour the wet ingredients into the dry and and stir until almost combined.

Add the apple pie filling and mix until the batter comes together completely.

Spread the batter into the prepared cake pan.

Sprinkle the streusel topping over the batter evenly.

Bake in the preheated oven for 45 minutes or until browned and an inserted toothpick comes out clean.

Cool on wire rack before serving.