Heat oven to 350°F (180°C) and fold a 7 x 7 inch (15 x15 cm) brownie pan with parchment paper.
Wash the strawberries and remove the top. With the help of a knife, dice them into small pieces.
In a large bowl, mash the ripe bananas. Add Greek yogurt, vanilla extract, 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. If the batter is too thick, add a splash of milk or more yogurt.
Fold the diced strawberries into the dough until fully incorporated.
Transfer the dough to the prepared baking pan and spread it out evenly. Top with sliced strawberries, 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.