Preheat the oven to 375°F (190°C) and lightly grease an 8×8-inch (20×20 cm) baking dish.
In a large bowl, mash the banana. Whisk in the plant-based milk, maple syrup, melted butter or oil, and vanilla.
Stir in the oats, baking powder, cinnamon, and salt until combined. Fold in any fruit, nuts, or other add-ins.
Pour the mixture into the prepared dish and spread evenly. Swirl in nut butter if using. Bake for 35–40 minutes, until golden on top and set in the center.
Let cool for 10–15 minutes before slicing. Serve warm with vegan yogurt or a splash of plant milk, and your favorite toppings like fresh fruit, nuts, or a drizzle of maple syrup.
