Preheat your oven to 350°F (175°C) and lightly grease a muffin tin or line it with muffin liners.
In a medium bowl, combine the rolled oats, almond milk, diced apples, honey (or maple syrup), cinnamon, vanilla extract, nutmeg, baking powder, and salt. Mix until everything is well incorporated.
If using, fold in the chopped walnuts or pecans for extra crunch and flavor.
Spoon the oatmeal mixture into the prepared muffin tin, filling each cup about 3/4 full.
Bake in the preheated oven for 20-25 minutes or until the tops are golden brown and a toothpick inserted into the center comes out clean.
Allow the oatmeal cups to cool in the tin for about 5 minutes, then gently remove and transfer to a wire rack to cool completely.
Notes
Serve warm, drizzled with honey and a sprinkle of cinnamon. Enjoy with fresh apple slices.