Preheat the oven to 350°F and generously spray donut pans with nonstick cooking spray.

In a medium bowl, mix pancake mix, brown sugar, cinnamon, and nutmeg. Ensure there are no lumps in the dry mix.

Add milk, egg, and melted butter to the dry mixture. Stir until combined, then add the diced apple and mix well.

Transfer the dough into a zipper bag or piping bag. Cut a triangle from the bag's end, making sure it's large enough for the apples to pass through. Pipe enough dough to fill each donut mold about 3/4 full as it will rise during baking. Alternatively, spoon the batter into each mold.

For the crumb topping, combine all crumb mixture ingredients in a small bowl. Use a fork to work the mixture into small crumbs. Avoid overworking to prevent a paste-like texture. Sprinkle the crumbs evenly and generously over each donut.

Bake for 12 minutes. Once done, let the donuts cool in the pan for 5 minutes before using an offset spatula to remove them. Dust with powdered sugar if desired. Serve warm or store in an airtight container for up to 3 days.