Prep your pan and oven. Heat the oven to 350°F (175°C). Line an 8x8-inch pan with parchment, leaving a little overhang for easy lifting. Lightly grease the sides.

Mix the dry ingredients. In a large bowl, combine rolled oats, oat flour, baking powder, salt, cinnamon, and ginger. Stir in cranberries and nuts or seeds so they’re well distributed.

Whisk the wet ingredients. In a separate bowl, mash the bananas until mostly smooth. Add nut butter, honey or maple syrup, oil, egg (or flax egg), and vanilla. Whisk until creamy.

Combine wet and dry. Pour the wet mixture into the dry mixture. Stir until no dry pockets remain. If the batter seems very thick or crumbly, add 2–3 tablespoons of milk to help it come together. You want a thick, scoopable mixture that holds when pressed.

Press into the pan. Transfer the mixture to the prepared pan. Use a spatula or lightly damp hands to press it evenly into the corners. Smooth the top so it bakes uniformly.

Bake. Bake for 22–28 minutes, until the edges are set and lightly golden and the center feels firm to the touch. A toothpick should come out with a few moist crumbs, not wet batter.

Cool completely. Let the pan cool on a rack for at least 30–45 minutes. This step helps the bars set and prevents crumbling when slicing.

Slice and serve. Lift the slab out by the parchment and cut into 9–12 bars. For cleaner cuts, use a sharp knife and wipe it between slices.