Preheat your oven to 375°F (190°C). This ensures a perfectly baked oatmeal with a golden top.
In a large mixing bowl, combine the old-fashioned rolled oats, ground cinnamon, baking powder, and kosher salt. Stir well to distribute the ingredients evenly.
In another bowl, whisk together the milk, egg, maple syrup, melted butter, and vanilla paste until well blended.
Pour the wet mixture into the bowl with the dry ingredients. Stir until just combined—don’t overmix!
Gently fold in the banana slices and blueberries, ensuring they are evenly distributed throughout the mixture.
Pour the oatmeal mixture into a greased baking dish, spreading it evenly.
Place the dish in the preheated oven and bake for 30-35 minutes, or until the top is golden and the center is set.
Remove from the oven and let it cool for a few minutes before slicing. Serve warm, topped with a drizzle of maple syrup or a dollop of yogurt if desired.