Step 1: Get oven ready. Preheat your oven to 375°F (190°C).
Step 2: Prep your pan. Line an 8x8-inch (20x20 cm) baking pan with parchment paper, leaving overhang on the sides. Alternatively, spray with nonstick cooking spray.
Step 3: Make the peach filling. In a large bowl, gently toss the diced peaches with the sugar, cornstarch (or tapioca starch), cinnamon, and orange juice. Stir to coat everything and set aside.
Step 4: Whip up the crumb. In a separate medium bowl, sift together the gluten-free flour blend, quick oats, brown sugar, cane sugar, and salt. Whisk to combine. Add the solid coconut oil, maple syrup, and coconut milk. Use a fork or pastry blender to work everything together until it looks like coarse crumbs.
Step 5: Form the base. Take about two-thirds (⅔) of the oat crumb mixture and sprinkle it evenly into the bottom of the prepared baking pan. Press it down firmly and evenly across the bottom using the bottom of a glass or flat measuring cup.
Step 6: Add the peachy layer. Pour the peach filling, including any collected juices, evenly over the pressed crust in the pan. Spread it out gently.
Step 7: Top it off. Take the remaining one-third (⅓) of the oat crumble mixture and sprinkle it loosely and evenly over the peach layer.
Step 8: Bake 'em! Pop the pan into the preheated oven. Bake for 40-45 minutes, or until the peaches are bubbling around the edges and the crumble topping is golden brown and set.
Step 9: Cool completely. Let the bars cool completely in the pan before slicing (at least 2-3 hours at room temperature). This is crucial for the filling to set and the bars to hold their shape. You can refrigerate to speed cooling.
Step 10: Slice and enjoy. Once completely cooled, use the parchment paper overhang to carefully lift the slab out of the pan. Place on a cutting board and slice into squares or rectangles.