Preheat your oven to 350°F (175°C). This ensures that your Peanut Butter Banana Baked Oatmeal bakes evenly and comes out perfectly cooked.
In a large mixing bowl, combine the old-fashioned oats, baking powder, ground cinnamon, and salt. Whisk these together until they are well mixed.
In another bowl, mash the ripe bananas until smooth. Add the creamy peanut butter, honey, egg, almond milk, and vanilla extract. Whisk these ingredients together until fully combined and creamy.
Pour the wet mixture into the bowl with the dry ingredients. Stir gently with a spatula until just combined. Be careful not to over-mix; you want to maintain the texture of the oats.
Grease your baking dish lightly with cooking spray or a bit of oil. Pour the oatmeal mixture into the prepared dish, spreading it evenly.
Place the baking dish in the preheated oven and bake for 25-30 minutes, or until the top is golden brown and a toothpick inserted in the center comes out clean.
Once baked, allow the oatmeal to cool for a few minutes. Cut into squares and serve warm, topped with banana slices, a drizzle of peanut butter, and a touch of honey if desired.