Preheat the oven to 350 degrees F. Mist a 9 x 9-inch square baking dish with nonstick cooking spray and set aside.
In a large bowl, whisk together the oats, baking powder, cinnamon, nutmeg, and salt.
In a separate bowl, whisk together the eggs, maple syrup, coconut oil, milk, and vanilla extract.
Add the wet ingredients to dry, and mix until combined. Stir in the chocolate chips (reserve a few to sprinkle over the top), coconut (reserve a tablespoon to sprinkle over the top), and walnuts until just combined; transfer to the preared baking dish and top with chocolate chips and coconut, if desired.
Bake for 35-40 minutes or until light golden on top and firm. Slice into 9 squares. Store leftovers in the refrigerator; serve warm, chilled, or at room temperature.