Preheat the oven to 350 degrees and line a muffin pan with liners.
Pour out the apple pie filling and cut the slices into bite-sized pieces.
Mix together the cake mix, apple pie filling, cinnamon and egg until just mixed.
Spoon the batter into the muffin pan and prepare the streusel topping by stirring together the flour, brown sugar, cinnamon, and butter until clumps begin to form. Sprinkle the topping over the top of each of the muffins.
Bake for 17 to 20 minutes, until a toothpick inserted in the center comes out clean.
Allow the muffins to cool in the pan until they’re safe to touch, then transfer them to a wire cooling rack to cool completely.