Heat oven to 350°F (180°C) and fold a 7 x 7 inch (15 x15 cm) brownie pan with parchment paper.
Wash, core and dice the apple into small pieces.
In a large bowl combine applesauce with yogurt, vanilla extract, cinnamon and a pinch of salt. For sweetener bars, add 2 to 4 tablespoons of maple syrup or honey to taste. Stir until smooth.
Add rolled oats and oat flour to the wet mixture, then stir until combined. Fold through the diced apple until it's fully incorporated into the dough.
Transfer the dough to the prepared baking pan and spread it out evenly. Top with more diced apple, if desired.
Bake in hot oven for 17 to 20 minutes, or until they have set in the center. Let cool to temperature, then slice into bars.