In a large bowl, whisk together all of the dry ingredients: oats, oat flour, flaxseed, cinnamon and salt.
In a medium bowl, whisk together the wet ingredients: coconut oil, peanut butter, maple syrup, coconut sugar and vanilla.
Pour the wet mixture over the dry mixture. Using a rubber spatula, stir and fold until well mixed. Fold in peanuts, if using.
Pour this mixture into the prepared baking pan. Using the rubber spatula, spread into an even, tightly-packed layer.
Bake for 16-24 minutes, until golden brown on top. Mine took 20 minutes. Place baking pan on a cooling rack, allowing to cool for 30 minutes. Then, pinch the edges of parchment/foil and lift bars onto the rack to continue cooling completely (about 1-2 hours). Slice into 16 bars. Enjoy!
A Note on Homemade Oat Flour: *If using homemade oat flour, make sure to blend the flour until very fine and sift the flour to remove coarse bits of oats that could create grainy bars.