Arrange oven rack in center position and preheat oven to 350°F. Grease a 9- by 13-inch baking dish with coconut oil or softened butter, or coat with non-stick cooking spray.
In a large bowl, whisk together the oats, flour, brown sugar, cinnamon, and salt. Stir in the coconut oil, honey, egg, and vanilla. Add the peanut butter and mix until well combined.
Scrape the batter into prepared baking dish and smooth the top so that it's an even thickness. Sprinkle with chopped peanuts and lightly press into the surface. Bake for 18 to 22 minutes or until the edges just start to turn golden brown. Allow to cool for at least 10 minutes before slicing into bars.
Cool completely and store in an airtight container.
To make oat flour, use a blender or mini food processor to grind 1 3/4 cups oats into a fine powder. Measure out 1 1/4 cups of oat flour for the recipe after grinding. If you have leftover oat flour after measuring, you can always save it for a Blueberry Muffin Healthy Oat Smoothie. :)
If desired, you may reduce the brown sugar.
To save a dirty dish, I melt the coconut oil in a measuring cup in the microwave and then measure the honey and vanilla on top. The coconut oil helps the honey slide out of the measuring cup.