01 - Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper, allowing for overhang to facilitate easy removal.
02 - In a substantial mixing bowl, thoroughly combine the rolled oats, whole wheat flour, baking powder, baking soda, ground cinnamon, ground nutmeg, and salt.
03 - In a separate bowl, whisk together the melted coconut oil, honey or maple syrup, unsweetened applesauce, large eggs, and vanilla extract until the mixture is smooth and well-emulsified.
04 - Pour the emulsified wet ingredients into the bowl containing the dry components. Stir gently until just incorporated, avoiding overmixing.
05 - Gently fold in the diced apples. If utilizing, also add the chopped nuts and raisins, distributing them evenly throughout the batter.
06 - Spread the prepared batter evenly into the prepared baking pan, ensuring a uniform layer.
07 - Bake for 28 to 32 minutes, or until the surface achieves a golden-brown hue and a toothpick inserted into the center emerges clean.
08 - Allow the baked bars to cool completely within the pan. Once cooled, carefully lift the assembled bars using the parchment overhang and cut them into 12 equal portions.