Preheat the oven to 350 °F and line an 8x8 baking pan with parchment paper.
Lightly beat the egg in a small bowl.
Combine the eggs, oats, and all remaining ingredients except the apples in a large bowl, mixing well with a rubber spatula. Add the diced apples and mix again. The mixture will be slightly wet.
Pour the oat mixture into the prepared pan and decorate with finely sliced apples. Bake for 30 to 35 minutes until the top is golden brown and the mixture is no longer wet.
Cool for a few minutes, slice, and enjoy!
Video
Notes
Storage
Refrigerate for up to 5 days in an airtight container.
Freeze slices wrapped in plastic wrap for up to 2 months in an airtight, freezer-safe container.
Defrost before reheating. Then, microwave individual portions at 1-minute intervals until warm.
Tips
Your oat mixture will be wet, and that's good. Just like traditional stovetop oats, baked oats need lots of moisture as they cook.
Coll the oats before slicing so they can fully set and hold their shape when you cut them into squares.
Rolled oats are best for this recipe. Quick oats don't have a hearty enough texture, and steel cuts won't bind as well.