01 - Preheat oven to 350°F (175°C) and grease a 9x9-inch baking dish.
02 - In a large mixing bowl, blend rolled oats, walnuts or pecans, baking powder, ground cinnamon, ground nutmeg, and salt until evenly distributed.
03 - In a separate bowl, whisk together the milk, eggs, melted butter or coconut oil, maple syrup or honey, and vanilla extract until smooth.
04 - Pour the wet mixture into the bowl with dry ingredients and gently stir until fully combined.
05 - Fold in the diced apples and raisins or dried cranberries, mixing gently to distribute fruit throughout the batter.
06 - Evenly transfer the mixture into the prepared baking dish, smoothing the top. Bake for 35 minutes, or until set and golden brown.
07 - Remove from oven and let cool for 5 minutes before serving. Serve warm with an optional splash of milk or dollop of yogurt.