In a separate bowl, ad the rolled oats, baking powder, salt, cinnamon, cardamom, and milk and stir until well incorporated. Add egg mixture to oat mixture and stir to combine. Transfer to a 9" baking pan. In a clean bowl, add the apple, nuts and maple syrup and mix together. Spread the topping over the oatmeal mixture. Bake for 25-35 minutes until golden brown. To serve, drizzle with syrup or applesauce.