Preheat the oven to 350F. Line an 8x8" baking pan with a strip of parchment paper that hangs out over the ends. Set this aside.
Place the peaches into a small pot with the lemon juice, sugar and water over medium-high heat. Once it comes to a simmer, reduce the heat and let it cook, stirring occasionally, until it's reduced down and thickened slightly. Then remove the pan from the heat, stir in the vanilla extract and set it aside.
In a large bowl, stir together both of the flours, oats, brown sugar, baking soda, cinnamon and salt. Then pour in the melted butter and stir until everything is moistened and incorporated. The mix should hold its shape if you squeeze some of it in your palm. Pour out 3/4 of the oat mix into the prepared baking pan and use your hands to flatten it out evenly and pack it down tightly.
Spread the peach mixture evenly over the bottom crust layer. Then sprinkle the rest of the dry mix evenly over the top. Bake uncovered for 20-25 minutes, until the top is golden brown. Then let it cool completely before slicing into bars and serving.
