Scoop out a small piece to mark the size your "bowl" -1/2" down, leaving at least ¼" of apple on the skin so your apple will hold up. Use an apple corer or small knife to remove center or a spoon, toss the core.
Scrape out the good portion of the apple and set aside in a bowl.
Stir oatmeal, brown sugar, cinnamon, and apple pie spice thoroughly. Stir in melted butter.
Dice the apple that was set aside. Measure 1 cup of diced apple and mix it into the oatmeal mixture.
Fill the apple with the oatmeal mixture, heaping it up on top.
Place filled apples in a baking dish and into the oven for 25-30 minutes, until apples are softened and topping is golden brown. Top with milk, cream, or syrup before serving if desired.
Recipe by Premeditated Leftovers™ at https://premeditatedleftovers.com/?p=25537