Preheat the oven to 375 degrees F (190 degrees C). Line a baking sheet with parchment paper.

Place oatmeal in a blender and process into a fine powder. Transfer to a large bowl and set aside.

Place coconut in the blender and process until finely chopped. Add to the bowl with the oatmeal. Add flour, baking powder, baking soda, and salt to the bowl; mix well and set aside.

Cream butter, brown sugar, and white sugar together in a bowl. Add egg and vanilla extract. Add butter mixture to the bowl with the flour mixture and mix well. Stir in white chocolate chips and macadamia nuts.

Roll heaping tablespoons of dough into balls and place on the prepared baking sheet.

Bake in the preheated oven until edges start to brown lightly, 12 to 14 minutes.