Gather all ingredients.
Preheat the oven to 350 degrees F (175 degrees C).
Core each apple, making a large well in the center; place onto a rimmed baking sheet.
Mix oats, brown sugar, and cinnamon together in a bowl; cut in butter until well combined. Spoon ¼ of the oat mixture into each apple.
Bake in the preheated oven until apples are tender and filling is bubbling, about 30 minutes.
