Preheat your oven to 350 degrees F.
In a large mixing bowl, combine white whole wheat flour, rolled oats, baking soda, cinnamon, pumpkin pie spice, salt, and both types of sugar. Mix these dry ingredients until they are well incorporated, and then set the bowl aside.
In a separate bowl, take the canned pumpkin, Greek yogurt, egg, and vanilla extract. Stir them together until they're combined and smooth.
Next, pour in the warm melted butter and stir it into the wet ingredients until fully combined.
Now, carefully mix the wet and dry ingredients together. It’s important not to over-mix; just combine until you can no longer see any dry flour.
Stir in the white chocolate chips or any other mix-ins you desire.
Take a 13x9 inch baking pan and line it with aluminum foil or parchment paper. Lightly spray it with a non-stick cooking spray.
Pour the batter into the prepared pan and spread it out evenly.
Place the pan in the preheated oven and bake for approximately 27 to 33 minutes.
Once baked, remove the bars from the oven and let them cool in the pan on a wire rack for at least ten minutes.
