Preheat Oven:
Preheat your oven to 375°F (190°C). Lightly grease an 8x8-inch baking dish with butter or coconut oil.
Combine Dry Ingredients:
In a large mixing bowl, stir together oats, baking powder, cinnamon, nutmeg, and salt.
Mix Wet Ingredients:
In a separate bowl, whisk milk, egg, maple syrup, melted butter, and vanilla extract until smooth.
Combine Wet and Dry:
Pour the wet mixture into the dry ingredients and mix gently until combined.
Add Apples and Nuts:
Fold in the diced apples and nuts, making sure they’re evenly distributed throughout the batter.
Pour and Bake:
Pour the mixture into the prepared dish. Smooth the top and bake for 30–35 minutes, or until golden and the center is just set.
Serve:
Serve warm straight from the oven, or let it cool and refrigerate for a quick breakfast bake later in the week.