Preheat your oven to 350°F (175°C) and grease a 9x9-inch baking dish or line it with parchment paper.
In a large bowl, combine the rolled oats, baking powder, cinnamon, and salt. Mix well.
In another bowl, whisk together the milk, peanut butter, maple syrup, eggs, and vanilla extract until smooth and well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Gently fold in the chopped bananas, chocolate chips, and nuts if using.
Pour the mixture into the prepared baking dish, spreading it evenly.
Bake for 25-30 minutes, or until the top is golden brown and a toothpick inserted in the center comes out clean.
Allow to cool for a few minutes before slicing into squares and serving.